Steam turbine power-generation plant and steam turbine

ABSTRACT

A compact steam turbine power-generation plant has a compact steam turbine that operates at a high temperature in a range of 600 to 660° C. Ferrite based heat resisting steels provide for thermal efficiency. The main steam temperature and the reheated steam temperature can be set in a range of 600 to 660° C. by making the main parts exposed to the high temperature atmosphere, such as the rotor shaft, from ferrite based forged steels and cast steels and by making a final stage blade of a low pressure turbine from a martensite steel. The final stage blade is made from a ferrite based forged steel having a tensile strength of 120 kgf/mm 2  or more; the rotor shaft is made from a ferrite based forged steel having a 10 5  h creep rupture strength of 11 kgf/mm 2  or more; and the inner casing is made from a ferrite based cast steel having a 10 5  h creep rupture strength of 10 kgf/mm 2  or more.

TECHNICAL FIELD

The present invention relates to a compact steam turbine andparticularly to a high temperature steam turbine in which a 12% Cr basedsteel is used for the final stage rotating blade of a low pressure steamturbine.

BACKGROUND ART

The rotating blade for a steam turbine is made from a 12Cr--Mo--Ni--V--Nsteel at the present time. In recent years, there is a desire to improvethe thermal efficiency of the gas turbine from the viewpoint of energysaving and to make the equipment of the gas turbine more compact fromthe viewpoint of space savings.

To improve the thermal efficiency of a gas turbine and to make theequipment thereof more compact, it is effective to make the blades ofthe steam turbine longer, and for this purpose, there has been atendency to make the length of the final stage blades of the lowpressure steam turbine becomes longer every year. With such a tendency,the service condition for the blades of a steam turbine becomes strict,and as a result the 12 Cr--Mo--Ni--V--N steel is no longer sufficient instrength under the above service conditions, and therefore, it isexpected that a new material will be developed having a higher strength.The strength of the material for the blades of the steam turbine isdetermined by its tensile strength which is a basic mechanicalcharacteristic.

The material for the blades of a steam turbine is also required toexhibit a high toughness in addition to a high strength for ensuringsafety against breakage.

As a structural material having a tensile strength higher than that ofthe conventional 12 Cr--Mo--Ni--V--N steel (martensite based steel),there are generally known a Ni based alloy and a Co based alloy;however, such materials are undesirable as blade materials because oftheir poor working ability at hot temperatures, poor machinability, andperiodic damping characteristic.

A disk material for a gas turbine is known, for example, from JapanesePatent Laid-open Nos. Sho 63-171856 and Hei 4-120246.

In the conventional steam turbine, the maximum steam temperature hasbeen set at 566° C. and the maximum steam pressure has been set at 246atg.

However, from the viewpoint of exhaustion of fossil fuel such as mineraloil or coal, energy saving, and prevention of environmental pollution,it is desired to increase the efficiency of the thermal power-generationplant, and to increase the efficiency of power-generation, it is mosteffective to increase the steam temperature of the steam turbine. Asuitable material for such a high efficient ultra-high temperature steamturbine is known from Japanese Patent Laid-open No. Hei 7-233704.

The present invention has been made to cope with the recent trend tomake the blades of a low pressure steam turbine longer. A suitablematerial for the rotating blades for a steam turbine is not disclosed inJapanese Patent Laid-open Nos. Sho 63-171856 and Hei 4-120246 at all.

Japanese Patent Laid-open No. Hei 7-233704 discloses a rotor material, acasing material, and the like; however, as described above, the documentdoes not describe a 12% Cr based martensite steel for a final stagerotating blade for a high pressure side turbine-intermediate pressureside turbine integral type steam turbine and a low pressure steamturbine which are operated at high temperatures.

An object of the present invention is to provide a steam turbineoperable at a high temperature in a range of 600 to 660° C. by use offerrite based heat resisting steels, to thereby enhance the thermalefficiency, and a steam turbine power-generation plant using the steamturbine.

Another object of the present invention is to provide a steam turbineoperable at each operating temperature in a range of 600 to 660° C. withits basic structure being substantially not changed, and a steam turbinepower-generation plant using the steam turbine.

DISCLOSURE OF INVENTION

The present invention provides a steam turbine power-generation plantincluding a combination of a high pressure turbine, an intermediatepressure turbine and two low pressure turbines, a combination of a highpressure turbine and a low pressure turbine connected to each other andan intermediate pressure turbine and a low pressure turbine connected toeach other, or a combination of a high pressure sideturbine-intermediate pressure side turbine integral steam turbine andone low pressure turbine or two low pressure turbines connected intandem with each other, in which the temperature of a steam inlet to afirst stage rotating blade of each of the high pressure turbine and theintermediate pressure turbine or the high pressure/intermediate pressureturbine is in a range of 600 to 660° C. (preferably, 600 to 620° C., 620to 630° C., 630 to 640° C.) and the temperature of a steam inlet to afirst stage rotating blade of the low pressure turbine is in a range of350 to 400° C., characterized in that a rotor shaft, rotating blades,stationary blades, and an inner casing, exposed to the temperatureatmosphere of the steam inlet, of each of the high pressure turbine andthe intermediate pressure turbine or the high pressure/intermediatepressure turbine are made from a high strength martensite steelcontaining Cr in an amount of 8 to 13 wt %; and a final stage rotatingblade of the low pressure turbine is specified such that a value of [thelength of a blade (inch)×the number of revolution (rpm)] is 125,000 ormore.

The present invention provides a steam turbine, particularly, a highpressure side turbine-intermediate pressure side turbine integral typesteam turbine in which steam discharged from a high pressure sideturbine is heated at a temperature equal to or higher than an inlettemperature on the high pressure side and fed in an intermediatepressure turbine, the steam turbine including a rotor shaft, rotatingblades planted in the rotor shaft, stationary blades for guiding flow ofsteam to the rotating blades, and an inner casing for holding thestationary blades, in which the temperature of the steam flowing to afirst stage one of the rotating blades is in a range of 600 to 660° C.and the pressure is 250 kgf/cm² or more (preferably 246 to 316 kgf/cm²)or 170 to 200 kgf/cm², characterized in that the rotor shaft or therotor shaft, at least a first stage one of the rotating blades, and afirst stage one of the stationary blades are made from a high strengthmartensite steel containing Cr in an amount of 9.5 to 13 wt %(preferably, 10.5 to 11.5 wt %) and having a full temper martensitestructure, the martensite steel being specified such that a 10⁵ h creeprupture strength thereof at a temperature corresponding to each steamtemperature (preferably, 610° C., 625° C., 640° C., 650° C., 660° C.) isin a range of 10 kgf/mm² or more (preferably, 17 kgf/mm² or more); andthe inner casing is made from a martensite cast steel containing Cr inan amount of 8 to 9.5 wt %, the martensite steel being specified suchthat the 10⁵ h creep rupture strength at the temperature correspondingto the steam temperature is in a range of 10 kgf/mm² or more(preferably, 10.5 kgf/mm² or more).

In the high pressure turbine and the intermediate pressure turbine orthe high pressure side turbine-intermediate pressure side turbineintegral type steam turbine, preferably, the rotor shaft, at least afirst stage one of the rotating blades, and a first stage one of thestationary blades, which are preferably used at a steam temperature of620 to 640° C., are made from a high strength martensite steelcontaining 0.05 to 0.20 wt % of C, 0.15 wt % or less of Si, 0.05 to 1.5wt % of Mn, 9.5 to 13 wt % of Cr, 0.05 to 1.0 wt % of Ni, 0.05 to 0.35wt % of V, 0.01 to 0.20 wt % of Nb, 0.01 to 0.06 wt % of N, 0.05 to 0.5wt % of Mo, 1.0 to 4.0 wt % of W, 2 to 10 wt % of Co, and 0.0005 to 0.03wt % of B, the balance being 78 wt % or more of Fe; and the rotor shaft,at least a first stage one of the rotating blades, and a first stage oneof the stationary blades, which are preferably used at a steamtemperature of 600 to less than 620° C., are made from a high strengthmartensite steel containing 0.1 to 0.25 wt % of C, 0.6 wt % or less ofSi, 1.5 wt % or less of Mn, 8.5 to 13 wt % of Cr, 0.05 to 1.0 wt % ofNi, 0.05 to 0.5 wt % of V, 0.10 to 0.65 wt % of W and 0.1 wt % or lessof Al, the balance being 80 wt % or more of Fe. Further, the above innercasing is preferably made from a high strength martensite steelcontaining 0.06 to 0.16 wt % of C, 0.5 wt % or less of Si, 1 wt % orless of Mn, 0.2 to 1.0 wt % of Ni, 8 to 12 wt % of Cr, 0.05 to 0.35 wt %of V, 0.01 to 0.15 wt % of Nb, 0.01 to 0.8 wt % of N, 1 wt % or less ofMo, 1 to 4 wt % of W, and 0.0005 to 0.003 wt % of B, the balance being85 wt % or more of Fe.

In the high pressure steam turbine according to the present invention,preferably, nine stages or more, preferably, ten stages or more of therotating blades are provided and the first stage one of the rotatingblades is of a double-flow type; and the rotor shaft is made from a highstrength martensite steel containing Cr in an amount of 9 to 13 wt %,the rotor shaft being specified such that a distance (L) between centersof bearings provided for the rotor shaft is 5000 mm or more (preferably,5100 to 6500 mm), the minimum diameter (D) of portions, of the rotorshaft, corresponding to the stationary blades is 660 mm or more(preferably, 680 to 740 mm), and the ratio (L/D) is in a range of 6.8 to9.9 (preferably, 7.9 to 8.7).

In the intermediate pressure steam turbine according to the presentinvention, preferably, the rotating blades have a double-flow structurein which two sets, each being composed of six stages or more of therotating blades, are symmetrically disposed right and left and a firststage one of the rotating blade is planted at the central portion of therotor shaft; and the rotor shaft is made from a high strength martensitesteel containing Cr in an amount of 9 to 13 wt %, the rotor shaft beingspecified such that a distance (L) between centers of bearings providedfor the rotor shaft is 5000 mm or more (preferably, 5100 to 6500 mm),the minimum diameter (D) of portions, of the rotor shaft, correspondingto the stationary blades is 630 mm or more (preferably, 650 to 710 mm),and the ratio (L/D) is in a range of 7.0 to 9.2 (preferably, 7.8 to8.3).

The present invention provides a low pressure steam turbine separatelyhaving a high pressure turbine and an intermediate pressure turbine,characterized in that the rotating blades has a double-flow structure inwhich two sets, each being composed of six stages or more of therotating blades, are symmetrically disposed right and left, and a firststage one of the rotating blades is planted at a central portion of therotor shaft; the rotor shaft is made from a Ni--Cr--Mo--V based lowalloy steel containing Ni in an amount of 3.25 to 4.25 wt %, the rotorshaft being specified such that a distance (L) between centers ofbearings provided for the rotor shaft is 6500 mm or more (preferably,6600 to 7100 mm), the minimum diameter (D) of portions, of the rotorshaft, corresponding to the stationary blades is 750 mm or more(preferably, 760 to 900 mm), and the ratio (L/D) is in a range of 7.8 to10.2 (preferably, 8.0 to 8.6); and a final stage one of the rotatingblades is made from a high strength martensite steel, the final stagerotating blade being specified such that a value of [the length of ablade (inch)×the number of revolution (rpm)] is 125,000 or more.

The present invention provides a steam turbine power-generation plantincluding a combination of a high pressure turbine, an intermediatepressure turbine and two low pressure turbines, a combination of a highpressure turbine and a low pressure turbine connected to each other andan intermediate pressure turbine and a low pressure turbine connected toeach other, or a combination of a high pressure sideturbine-intermediate pressure side turbine integral steam turbine andone low pressure turbine or two low pressure turbines connected intandem with each other, in which the temperature of a steam inlet to afirst stage rotating blade of each of the high pressure turbine and theintermediate pressure turbine or the high pressure/intermediate pressureturbine is in a range of 600 to 660° C. and the temperature of a steaminlet to a first stage rotating blade of the low pressure turbine is ina range of 350 to 400° C.; the metal temperature of each of the firststage rotating blade planted portion and the first stage rotating bladeof the rotor shaft of the high pressure turbine is not allowed to belower, 40° C. or more, than the temperature of the steam inlet to thefirst stage rotating blade of the high pressure turbine (preferably,lower 20-35° C. than the steam temperature); and the metal temperatureof each of the first stage rotating blade planted portion and the firststage rotating blade of the rotor shaft of the intermediate pressureturbine is not allowed to be lower, 75° C. or more, than the temperatureof the steam inlet to the first stage rotating blade of the intermediatepressure turbine (preferably, lower 50-70° C. than the steamtemperature), characterized in that the rotor shaft and at least thefirst stage rotating blade of each of the high pressure turbine and theintermediate pressure turbine are made from a martensite steelcontaining Cr in an amount of 9.5 to 13 wt %; and a final stage one ofthe rotating blades is made from a high strength martensite steel, thefinal stage rotating blade being specified such that a value of [thelength of a blade (inch)×the number of revolution (rpm)] is 125,000 ormore.

The present invention provides a coal burning thermal power-generationplant including a coal burning boiler, a steam turbine driven by steamproduced by the boiler, a single or double generators driven by thesteam turbine to generate a power of 1000 MW or more, characterized inthat the steam turbine has a combination of a high pressure turbine, anintermediate pressure turbine and two low pressure turbines, acombination of a high pressure turbine and a low pressure turbineconnected to each other and an intermediate pressure turbine and a lowpressure turbine connected to each other, or a combination of a highpressure side turbine-intermediate pressure side turbine integral steamturbine and one low pressure turbine or two low pressure turbinesconnected in tandem with each other; the temperature of a steam inlet toa first stage rotating blade of each of the high pressure turbine andthe intermediate pressure turbine or the high pressure/intermediatepressure turbine is in a range of 600 to 660° C. and the temperature ofa steam inlet to a first stage rotating blade of the low pressureturbine is in a range of 350 to 400° C.; steam heated at a temperaturehigher 3° C. or more (preferably, 3 to 10° C., more preferably, 3 to 7°C.) than the temperature of the steam inlet to the first stage rotatingblade of the high pressure turbine by a superheater of the boiler isallowed to flow to the first stage rotating blade of the high pressureturbine; the steam discharged from the high pressure turbine is heatedat a temperature higher 2° C. or more (preferably, 2 to 10° C., morepreferably, 2 to 5° C.) than the temperature of the steam inlet of thefirst stage rotating blade of the intermediate pressure blade by are-heater of the boiler and is allowed to flow to the first stagerotating blade of the intermediate pressure turbine; and the steamdischarged from the intermediate pressure turbine is heated at atemperature higher 3° C. or more (preferably, 3 to 10° C., morepreferably, 3 to 6° C.) than the temperature of the steam inlet to thefirst stage rotating blade of the low pressure turbine by an economizerof the boiler and is allowed to flow to the first stage rotating bladeof the low pressure turbine; and a final stage one of the rotatingblades of the low pressure turbine is made from a high strengthmartensite steel, the final stage rotating blade being specified suchthat a value of [the length of a blade (inch)×the number of revolution(rpm)] is 125,000 or more.

In the above low pressure steam turbine having the high pressure turbineand the intermediate pressure turbine or the high pressure/intermediatepressure integral turbine, preferably, the temperature of a steam inletto a first stage one of the rotating blades is in a range of 350 to 400°C. (preferably, 360 to 380° C.); and the rotor shaft is made from a lowalloy steel containing 0.2 to 0.3 wt % of C, 0.05 wt % or less of Si,0.1 wt % or less of Mn, 3.25 to 4.25 wt % of Ni, 1.25 to 2.25 wt % ofCr, 0.07 to 0.20 wt % of Mo, and 0.07 to 0.2 wt % of V, the balancebeing 92.5 wt % of or more of Fe.

In the above high pressure steam turbine, preferably, seven stages ormore (preferably, nine to twelve stages) of the rotating blades areprovided; the length of a blade portion of each of the rotating bladesarranged from the upstream side to the downstream side of the steam flowis in a range of 25 to 180 mm; the diameter of a rotating blade plantedportion of the rotor shaft is larger than the diameter of a portion, ofthe rotor shaft, corresponding to the stationary shaft; the axial rootwidth of the rotating blade planted portion becomes stepwise larger fromthe upstream side to the downstream side in three steps or more(preferably, in four to seven steps); the ratio of the axial root widthof the rotating blade planted portion to the length of the blade portionis in a range of 0.2 to 1.6 (preferably, 0.30 to 1.30, more preferably,0.65 to 0.95) and becomes smaller from the upstream side to thedownstream side.

In the above high pressure steam turbine, preferably, seven stages ormore (preferably, nine stages or more) of the rotating blades areprovided; the length of a blade portion of each of the rotating bladesarranged from the upstream side to the downstream side of the steam flowis in a range of 25 to 180 mm; and the ratio between the lengths of theblade portions of the adjacent ones of the rotating blades is in a rangeof 2.3 or less and becomes gradually larger to the downstream side, andthe length of the blade portion becomes larger from the upstream side tothe downstream side.

In the above high pressure steam turbine, preferably, seven stages ormore (preferably, nine stages or more) of the rotating blades areprovided; the length of a blade portion of each of the rotating bladesarranged from the upstream side to the downstream side of the steam flowis in a range of 25 to 180 mm; and the axial width of a portion, of therotor shaft, corresponding to the stationary blade becomes stepwisesmaller from the upstream side to the downstream side in two steps ormore (preferably, in two to four steps), and the ratio of the aboveaxial width to the length of the blade portion of the rotating blade onthe downstream side is in a range of 4.5 or less and becomes stepwisesmaller to the downstream side.

In the above intermediate pressure steam turbine, preferably, therotating blades have a double-flow structure in which two steps, eachbeing composed of six stages or more (preferably, six to nine stages) ofthe rotating blades, are symmetrically disposed right and left; thelength of a blade portion of each of the rotating blades arranged fromthe upstream side to the downstream side of the steam flow is in a rangeof 60 to 300 mm; the diameter of a rotating blade planted portion of therotor shaft is larger than the diameter of a portion, of the rotorshaft, corresponding to the stationary shaft; the axial root width ofthe rotating blade planted portion becomes stepwise larger from theupstream side to the downstream side in two steps or more (preferably,in two to six steps); the ratio of the axial root width of the rotatingblade planted portion to the length of the blade portion is in a rangeof 0.35 to 0.80 (preferably, 0.5 to 0.7) and becomes smaller from theupstream side to the downstream side.

In the above intermediate pressure steam turbine, preferably, therotating blades have a double-flow structure in which two steps, eachbeing composed of six stages or more of the rotating blades, aresymmetrically disposed right and left; the length of a blade portion ofeach of the rotating blades arranged from the upstream side to thedownstream side of the steam flow is in a range of 60 to 300 mm; and thelength of the blade portion becomes larger from the upstream side to thedownstream side, and the ratio between the lengths of the blade portionsof the adjacent ones of the rotating blades is in a range of 1.3 or less(preferably, 1.1 to 1.2) and becomes gradually larger to the downstreamside.

In the above intermediate pressure steam turbine, preferably, therotating blades have a double-flow structure in which two steps, eachbeing composed of six stages or more of the rotating blades, aresymmetrically disposed right and left; the length of a blade portion ofeach of the rotating blades arranged from the upstream side to thedownstream side of the steam flow is in a range of 60 to 300 mm; and theaxial width of the portion, of the rotor shaft, corresponding to thestationary blade becomes stepwise smaller from the upstream side to thedownstream side in two steps or more (preferably, in three to sixsteps), and the ratio of the above axial width to the length of theblade portion of the rotating blade on the downstream side is in a rangeof 0.80 to 2.50 (preferably, 1.0 to 2.0) and becomes stepwise smaller tothe downstream side.

In the above low pressure steam turbine in the power-generation plant inwhich the high pressure turbine and the-intermediate pressure turbineare separately provided, preferably, the rotating blades have adouble-flow structure in which two steps, each being composed of sixstages or more (preferably, eight to ten stages) of the rotating blades,are symmetrically disposed right and left; the length of a blade portionof each of the rotating blades arranged from the upstream side to thedownstream side of the steam flow is in a range of 80 to 1300 mm; thediameter of a rotating blade planted portion of the rotor shaft islarger than the diameter of a portion, of the rotor shaft, correspondingto the stationary shaft; the axial root width of the rotating bladeplanted portion becomes stepwise larger from the upstream side to thedownstream side in three steps or more (preferably, in four to sevensteps); and the ratio of the axial root width of the rotating bladeplanted portion to the length of the blade portion is in a range of 0.2to 0.7 (preferably, 0.3 to 0.55) and becomes smaller from the upstreamside to the downstream side.

In the above low pressure steam turbine in the power-generation plant inwhich the high pressure turbine and the intermediate pressure turbineare separately provided, preferably, the rotating blades have adouble-flow structure in which two sets, each being composed of sixstages or more of the rotating blades, are symmetrically disposed rightand left; the length of a blade portion of each of the rotating bladesarranged from the upstream side to the downstream side of the steam flowis in a range of 80 to 1300 mm; and the length of the blade portionbecomes larger from the upstream side to the downstream side, and theratio between the lengths of the blade portions of the adjacent ones ofthe rotating blades is in a range of 1.2 to 1.8 (preferably, 1.4 to 1.6)and becomes gradually larger to the downstream side.

In the above low pressure steam turbine, preferably, the rotating bladeshave a double-flow structure in which two sets, each being composed ofsix stages or more, preferably, eight stages or more of the rotatingblades, are symmetrically disposed right and left; the length of a bladeportion of each of the rotating blades arranged from the upstream sideto the downstream side of the steam flow is in a range of 80 to 1300 mm;the axial width of the portion, of the rotor shaft, corresponding to thestationary blade becomes stepwise larger from the upstream side to thedownstream side, preferably, in three stages or more (more preferably,four to seven stages); and the ratio between the lengths of the bladeportions of the adjacent ones of the rotating blades is in a range of0.2 to 1.4 (preferably, 0.25 to 1.25, more preferably, 0.5 to 0.9) andbecomes stepwise smaller to the downstream side.

In the above high pressure steam turbine, seven stages or more,preferably, nine stages or more of the rotating blades are provided; thediameter of the portion, of the rotor shaft, corresponding to thestationary blade is smaller than the rotating blade planted portion ofthe rotor shaft; the axial width of the portion corresponding to thestationary blade becomes stepwise larger from the downstream side to theupstream side of the steam flow in two steps or more (preferably, two orfour steps); the width of the portion corresponding to the stationaryblade between the final stage rotating blade and the preceding stagerotating blade is 0.75 to 0.95 times (preferably, 0.8 to 0.9 times, morepreferably, 0.82 to 0.88 times) the width between the second stagerotating blade and the third stage rotating blade; the axial width ofthe rotating blade planted portion of the rotor shaft becomes stepwiselarger from the upstream side to the downstream side of the steam flowin three steps or more (preferably, four to seven steps); and the axialwidth of the final stage rotating blade is 1 to 2 times (preferably, 1.4to 1.7 times) the axial width of the second stage rotating blade.

In the above intermediate pressure steam turbine, preferably, six stagesor more the rotating blades are provided; the diameter of the portion,of the rotor shaft, corresponding to the stationary blade is smallerthan the diameter of the rotating blade planted portion of the rotorshaft; the axial width of the portion corresponding to the stationaryblade becomes stepwise larger from the downstream side to the upstreamside of the steam flow in two steps or more (preferably, three or sixsteps); the width of the portion corresponding to the stationary bladebetween the final stage rotating blade and the preceding stage rotatingblade is 0.5 to 0.9 times (preferably, 0.65 to 0.75 times) the widthbetween the first stage rotating blade and the second stage rotatingblade; the axial width of the rotating blade planted portion of therotor shaft becomes stepwise larger from the upstream side to thedownstream side of the steam flow in two steps or more (preferably,three to six steps); and the axial width of the final stage rotatingblade is 0.8 to 2 times (preferably, 1.2 to 1.5 times) the axial widthof the final stage rotating blade.

In the above low pressure steam turbine, the rotating blades have adouble-flow structure in which two sets, each being composed of eightstages or more of the rotating blades, are symmetrically disposed rightand left; the diameter of the portion, of the rotor shaft, correspondingto the stationary blade is smaller than the rotating blade plantedportion of the rotor shaft; the axial width of the portion correspondingto the stationary blade becomes stepwise larger from the downstream sideto the upstream side of the steam flow, preferably, in three steps ormore (more preferably, four or seventh steps); the width of the portioncorresponding to the stationary blade between the final stage rotatingblade and the preceding stage rotating blade is 1.5 to 3.0 times(preferably, 2.0 to 2.7 times) the width between the first stagerotating blade and the second stage rotating blade; the axial width ofthe rotating blade planted portion of the rotor shaft becomes stepwiselarger from the upstream side to the downstream side of the stem flow,preferably, in three steps or more (preferably, four to seven steps);and the axial width of the final stage rotating blade is 5 to 8 times(preferably, 6.2 to 7.0 times) the axial width of the final stagerotating blade.

Each of the above high pressure turbine, intermediate pressure turbine,high pressure/intermediate pressure integral turbine, and low pressureturbine can be used at each of service steam temperatures in a range of610 to 660° C. with the same structure.

It is desired to adjust the composition of the rotor material of thepresent invention, having a full temper martensite structure, such thatthe Cr equivalent calculated by the following equation is set in a rangeof 4 to 8 wt % for obtaining a high temperature strength, a high lowtemperature toughness, and a high fatigue strength.

The high pressure side turbine-intermediate pressure side turbineintegral type steam turbine of the present invention is characterized inthat seven stages or more, preferably, eight stages or more of therotating blades are provided on the high pressure side and five stagesor more, preferably, six stages or more of the rotating blades areprovided on the intermediate pressure side; and the rotor shaft is madefrom a high strength martensite steel containing Cr in an amount of 9 to13 wt %, the rotor shaft being specified such that a distance (L)between centers of bearings provided for the rotor shaft is 6000 mm ormore (preferably, 6100 to 7000 mm), the minimum diameter (D) ofportions, of the rotor shaft, corresponding to the stationary blades is660 mm or more (preferably, 620 to 760 mm), and the ratio (L/D) is in arange of 8.0 to 11.3 (preferably, 9.0 to 10.0).

The low pressure steam turbine used in combination with the highpressure/intermediate pressure integral type turbine has the followingfeature. In the low pressure steam turbine, the rotating blades have adouble-flow structure in which two sets, each being composed of fivestages or more, preferably, six stages or more of the rotating blades,are symmetrically disposed right and left, and a first stage one of therotating blades is planted at a central portion of the rotor shaft; therotor shaft is made from a Ni--Cr--Mo--V based low alloy steelcontaining Ni in an amount of 3.25 to 4.25 wt %, the rotor shaft beingspecified such that a distance (L) between centers of bearings providedfor the rotor shaft is 6500 mm or more (preferably, 6600 to 7500 mm),the minimum diameter (D) of portions, of the rotor shaft, correspondingto the stationary blades is 750 mm or more (preferably, 760 to 900 mm),and the ratio (L/D) is in a range of 7.8 to 10.0 (preferably, 8.0 to9.0); and a final stage one of the rotating blades is made from a highstrength martensite steel, the final stage rotating blade beingspecified such that a value of [the length of a blade (inch)×the numberof revolution (rpm)] is 125,000 or more.

The above rotor shaft is made from a low alloy steel containing 0.2 to0.3 wt % of C, 0.05 wt % or less of Si, 0.1 wt % or less of Mn, 3.0 to4.5 wt % of Ni, 1.25 to 2.25 wt % of Cr, 0.007 to 0.20 wt % of Mo, and0.07 to 0.2 wt % of V, the balance being 92.5 wt % or more of Fe, therotor shaft being specified such that the diameter (D) of the portion,of the rotor shaft, corresponding to the stationary blade is in a rangeof 750 to 1300 mm and the diameter (L) between centers of bearingsprovided for the rotor shaft is 5.0 to 9.5 times the diameter (D).

The above rotating blades have a double-flow structure in which twosets, each being composed of five stages or more, preferably, six stagesor more of the rotating blades are symmetrically provided right andleft; the length of a blade portion of each of the rotating bladesarranged from the upstream side to the downstream of the steam flow isin a range of 80 to 1300 mm; the diameter of the rotating blade plantedportion of the rotor shaft is larger the diameter of the portion, of therotor shaft, corresponding to the stationary blade; the axial root widthof the rotating blade planted portion of the rotor shaft is extendeddownward to be larger than the blade planted portion and becomesstepwise smaller from the downstream side to the upstream side; and theratio of the axial root width of the rotating blade planted portion tothe length of the blade portion is in a range of 0.25 to 0.80.

The above rotating blades has a double-flow structure in which two sets,each being composed of five stages or more, preferably, six stages ormore of the rotating blades are symmetrically provided right and left;the length of a blade portion of each of the rotating blades is in arange of 80 to 1300 mm and becomes gradually larger from the upstreamside to the downstream side; and the ratio between the lengths of theblade portions of the adjacent ones of the rotating blades is in a rangeof 1.2 to 1.7.

The above rotating blades has a double-flow structure in which two sets,each being composed of five stages or more, preferably, six stages ormore of the rotating blades are symmetrically provided right and left;the length of a blade portion of each of the rotating blades is in arange of 80 to 1300 mm and becomes larger from the upstream side to thedownstream side; the axial root width of the rotating blade plantedportion of the rotor shaft becomes larger from the upstream side to thedownstream side at least in three steps, and is extend downward to belarger than the width of the rotating blade planted portion.

The high pressure side turbine-intermediate pressure side turbineintegral type steam turbine according to the present invention has thefollowing configuration:

Seven stages or more of the rotating blades are provided on the highpressure side; the length of a blade portion of each of the rotatingblades arranged from the upstream side to the downstream side of thesteam flow is in a range of 40 to 200 mm; the diameter of a rotatingblade planted portion of the rotor shaft is larger than the diameter ofa portion, of the rotor shaft, corresponding to the stationary shaft;the axial root width of the rotating blade planted portion becomesstepwise larger from the upstream side to the downstream side; the ratioof the axial root width of the rotating blade planted portion to thelength of the blade portion is in a range of 0.20 to 1.60, preferably,0.25 to 1.30 and becomes larger from the upstream side to the downstreamside; and two sets, each being composed of five stages or more of therotating blades, are symmetrically provided right and left on theintermediate pressure side; the length of a blade portion of each of therotating blades arranged from the upstream side to the downstream sideof the steam flow is in a range of 100 to 350 mm; the diameter of arotating blade planted portion of the rotor shaft is larger than thediameter of a portion, of the rotor shaft, corresponding to thestationary shaft; the axial root width of the rotating blade plantedportion becomes smaller from the upstream side to the downstream sideexcept for the final stage; the ratio of the axial root width of therotating blade planted portion to the length of the blade portion is ina range of 0.35 to 0.80, preferably, 0.40 to 0.75 and becomes smallerfrom the upstream side to the downstream side.

Further, seven stages or more of the rotating blades are provided on thehigh pressure side; the length of a blade portion of each of therotating blades arranged from the upstream side to the downstream sideof the steam flow is in a range of 25 to 200 mm; and the ratio betweenthe lengths of the blade portions of the adjacent ones of the rotatingblades is in a range of 1.05 to 1.35 and the length of the blade portionof 100 to 350 mm; and the ratio between the blade portions becomesgradually larger from the upstream side to the downstream side; and fivestages or more of the rotating blades are provided on the intermediatepressure portion; the length of a blade portion of each of the rotatingblades arranged from the upstream side to the downstream side is in arange of the adjacent ones of the rotating blades is in a range of 1.10to 1.30 and the length of the blade portion of the rotating bladebecomes gradually larger from the upstream side to the downstream side.

Further, six stages or more, preferably, seven stages or more of therotating blades are provided on the high pressure side; the diameter ofthe portion, of the rotor shaft, corresponding to the stationary bladeis smaller than the diameter of the rotating blade planted portion ofthe rotor shaft; the axial root width of the rotating blade portion iswidest at the first stage and becomes stepwise larger from the upstreamside to the downstream side in two steps or more, preferably, in threesteps or more; five stages or more of the rotating blades are providedon the intermediate pressure side; the diameter of the portion, of therotor shaft, corresponding to the stationary blade is smaller than thediameter of the rotating blade planted portion of the rotor shaft; theaxial root width of the rotating blade portion is stepwise changed onthe upstream side as compared with the downstream side, preferably, infour steps or more; and the axial root width at the first stage islarger than that at the second stage, the axial root width at the finalstage is larger than that at each of the other stages, and the axialroot width at each of the first stage and the second stage is extendeddownward.

The present invention provides a steam turbine long blade characterizedin that the steam turbine is made from a martensite steel containing0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less ofMn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % or less of Ni, 1.5 to 3.0 wt %of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of one kind ortwo kinds of Nb and Ta, and 0.02 to 0.10 wt % of N.

The above steam turbine long blade, which is required to withstand ahigh centrifugal force and a vibrational stress caused by high speedrotation, must be high in both the tensile strength and high cyclicfatigue strength. Consequently, the blade material is required to have afull temper martensite structure for eliminating the undesirable δferrite which significantly reduces the fatigue strength.

The inventive steel is characterized in that it does not contain a δferrite phase substantially by adjusting the composition such that theCr equivalent calculated by the above equation is 10 or less.

The tensile strength of the long blade material steel is 120 kgf/mm² ormore, preferably, 128.5 kgf/mm² or more.

To obtain a steam turbine long blade material which is homogeneous andhigh in strength, a forged product obtained from an ingot is subjectedto the following heat-treatments [(quenching and temper (twice)];namely, the product is kept at a temperature of 1000 to 1100° C.,preferably, for 0.5 to 3 h and is rapidly cooled to room temperature(quenching), and heated to a temperature of 550 to 570° C. and kept atthe temperature, preferably, for 1 to 6 h and cooled to room temperature(primary temper) and then heated to a temperature of 560 to 590° C. andkept at the temperature, preferably, for 1 to 6 h and cooled to roomtemperature (secondary temper).

According to the present invention, in the steam turbine (number ofrevolution: 3600 rpm), the length of the final stage blade portion ofthe low pressure turbine is set at 914 mm (36") or more, preferably, 965mm (38") or more; and in the steam turbine (number of revolution: 3000rpm), the length of the final stage blade portion of the low pressureturbine is set at 1092 mm (43") or more, preferably, 1168 mm (46") ormore. Further, [the length of a blade portion (inch)]×the number ofrevolution (rpm)] is set at 125,000 or more, preferably, 138,000 ormore.

In the heat resisting cast steel as the casing material according to thepresent invention, to enhance the high temperature strength, lowtemperature toughness and fatigue strength by adjusting the alloycomposition such that the alloy has a temper martensite of 95% or more(δ ferrite: 5% or less), the alloy composition is preferably adjustedsuch that the Cr equivalent calculated by the following equation (thecontent of each element is expressed in wt %) is in a range of 4 to 10.

    Cr equivalent=Cr+6Si+4Mo+1.5W+11V+5Nb-40C-30N-30B-2Mn-4Ni-2Co+2.5Ta

In the 12 Cr based heat resisting steel of the present invention,particularly, when used in steam at a temperature of 625° C. or more,the material preferably exhibits a 10⁵ h creep rupture strength of 10kgf/mm² or more and an impact absorption energy (at room temperature) of1 kgf-m or more.

(1) There will be described the reason for limiting the content of eachcomponent of the 12% Cr based steel used for the final stage blade ofthe low pressure steam turbine according to the present invention.

C is required to be added in an amount of 0.08 wt % at minimum forensuring the tensile strength. When C is added in an excessively largeamount, the toughness is reduced. The content of C must be 0.20 wt % orless. In particular, the content of C is, preferably, 0.10 to 0.18 wt %,more preferably, 0.12 to 0.16 wt %.

Si and Mn are added upon melting of steel as a deoxidizer and adeoxidizing/desulfurizing agent, respectively. Such an effect can beobtained by addition of the element in a small amount. Si is a δ ferritegenerating element, and therefore, the addition of Si in a large amountmay cause undesirable δ ferrite which acts to reduce the fatigue andtoughness. The content of Si must be 0.25 wt % or less. In the case ofadopting a carbon/vacuum deoxidation process or an electroslag meltingprocess, Si is not required to be added, and rather Si may be not added.In particular, the content of Si may be in a range of 0.10 wt % or less,preferably, in a range of 0.05 wt % or less.

The addition of Mn in a large amount reduces the toughness. The contentof Mn must be 0.9 wt % or less. In particular, to improve the toughness,the content of Mn, which is effective as a deoxidizer, may in a range of0.4 wt % or less, preferably, 0.2 wt % or less.

Cr is effective to increase the corrosion resistance and tensilestrength of the alloy; however, the addition of Cr in an amount of 13 wt% or more may cause a δ ferrite structure. The addition of Cr in anamount of less than 8 wt % is insufficient for Cr to exhibit the effectof increasing the corrosion resistance and tensile strength. The contentof Cr may be in a range of 8 to 13 wt %. To improve the strength, thecontent of Cr is preferably in a range of 10.5 to 12.5 wt %, morepreferably, 11 to 12 wt %.

Mo is effective to increase the tensile strength of the alloy by itsfunction of promoting solid-solution and precipitation. Such an effect,however, is not large so much, and the addition of Mo in an amount of 3wt % or more may cause δ ferrite. The content of Mo is limited in arange of 1.5 to 3.0 wt %. In particular, the content of Mo is preferablyin a range of 1.8 to 2.7 wt %, more preferably, 2.0 to 2.5 wt %. It isto be noted that W and Co have the same effect as that of Mo.

V and Nb are effective to enhance the tensile strength and improve thetoughness by the function of precipitating carbides. When the content ofV is 0.05 wt % or less and the content of Nb is 0.02 wt % or less, theabove effect is insufficient. The addition of V in an amount of 0.35 wt% or more and Nb in an amount of 0.2 wt % or more may cause δ ferrite.In particular, the content of V may be in a range of 0.15 to 0.30 wt %,preferably, 0.25 to 0.30 wt %; and the content of Nb may be in a rangeof 0.04 to 0.15 wt %, preferably, 0.06 to 0.12 wt %. It is to be notedthat Ta may be added in place of or in combination with Nb.

Ni is effective to enhance the low temperature toughness and preventoccurrence of δ ferrite. When the content of Ni is 2 wt % or less, theeffect cannot be sufficiently obtained. When it is more than 3 wt %, theaddition effect is saturated. In particular, the content of Ni ispreferably in a range of 2.3 to 2.9 wt %, more preferably, 2.4 to 2.8 wt%.

N is effective to improve the tensile strength and prevent occurrence ofδ ferrite. When the content of N is less than 0.02 wt %, the effectcannot be sufficiently obtained. When it is more than 0.1 wt %, thetoughness is reduced. In particular, the content of N is preferably in arange of 0.04 to 0.08 wt %, more preferably, 0.06 to 0.08 wt %.

The reduction in contents of Si, P and S is effective to increase thelow temperature toughness while ensuring the tensile. The contents ofSi, P and S are desired to be reduced as much as possible. To improvethe low temperature toughness, the content of Si may be in a range of0.1 wt % or less; the content of P may be in a range of 0.015 wt % orless; and the content of S may be in a range of 0.015 wt % or less. Inparticular, the content of Si is preferably in a range of 0.05 wt % orless; the content of P is preferably in a range of 0.010 wt % or less;and the content of S is preferably in a range of 0.010 wt % or less. Thereduction in contents of Sb, Sn and As is also effective to increase thelow temperature toughness, and therefore, the contents of Sb, Sn and Asare desired to be reduced as much as possible. However, in considerationof the existing steel-making technical level, the content of Sb may bein a range of 0.0015 wt % or less; the content of Sn may be in a rangeof 0.01 wt % or less; and the content of As may be in a range of 0.02 wt% or less. In particular, the content of Sb is preferably in a range of0.001 wt % or less; the content of Sn is preferably in a range of 0.005wt % or less; and the content of As is preferably in a range of 0.01 wt% or less.

According to the present invention, the ratio (Mn/Ni) is preferably in arange of 0.11 or less.

The heat-treatment of the inventive material is preferably performed byuniformly heating the material at a temperature allowing perfectaustenite transformation, that is, in a range of 1000 to 1100° C.,followed by rapid cooling (preferably, oil-cooling) of the material;heating and keeping to and at a temperature of 550 to 570° C., followedby cooling of the material (primary temper); and heating and keeping toand at a temperature of 560 to 680° C., followed by cooling of thematerial (secondary temper), to thereby obtain a full temper martensitestructure.

(2) There will be described a reason for limiting the content of eachcomponent of the ferrite based heat resisting steel, which is used for arotor, blade, nozzle, inner casing fastening bolt and an intermediatepressure portion initial diaphragm in a high pressure turbine, anintermediate presssure turbine or a high pressure/intermediate pressureturbine of the inventive steam turbine operable at a temperature of 620to 640° C.

C is an essential element for increasing the high temperature strengthby ensuring the quenching ability and precipitating carbides at thetempering step. Also, to obtain the high tensile strength, C is requiredto be added in an amount of 0.05 wt % or more. However, when the contentof C is more than 0.20 wt %, the metal structure becomes unstable uponthe alloy is exposed to a high temperature atmosphere for a long time,to reduce the long time creep rupture strength. The content of C islimited in a range of 0.05 to 0.20 wt %, and is preferably in a range of0.08 to 0.13 wt %, more preferably, 0.09 to 0.12 wt %.

Mn is added as a deoxidizer and the like. The effect can be obtained bythe addition of Mn in a small amount. The addition of Mn in a largeamount more than 1.5 wt % is undesirable because it reduces the creeprupture strength. In particular, the content of Mn is preferably in arange of 0.03 to 0.20 wt %, or in a range of 0.3 to 0.7 wt %, morepreferably, 0.35 to 0.65 wt %. The smaller content of Mn is effective toincrease the strength, and the larger content of Mn is effective toimprove machinability.

Si is added as a deoxidizer. However, in the case of adopting thesteel-making technique such as carbon/vacuum deoxidization process,deoxidization by Si becomes unnecessary. The reduction in content of Siis effective to prevent occurrence of the undesirable δ ferritestructure and to prevent reduction in toughness due to segregation atcrystal boundaries and the like. As a result, if Si is added, thecontent of Si should be limited in a range of 0.15 wt % or less,preferably, 0.07 wt % or less, more preferably, less than 0.04 wt %.

Ni is very effective to increase the toughness and prevent occurrence ofδ ferrite. The effect cannot be sufficiently obtained by addition of Niin an amount of less than 0.05 wt %. Meanwhile, the addition of Ni in anamount more than 1.0 wt % is undesirable because it reduces the creeprupture strength. In particular, the content of Ni is preferably in arange of 0.3 to 0.7 wt %, more preferably, 0.4 to 0.65 wt %.

Cr is an essential element for increasing the high temperature strengthand the high temperature oxidation resistance. To achieve the effect, Crmust be added in an amount of 9 wt % at minimum. The addition of Cr inan amount more than 13 wt % may cause the undesirable δ ferritestructure, leading to reduction in the high temperature strength andtoughness. The content of Cr is limited in a range of 9 to 12 wt %,preferably, in a range of 10 to 12 wt %, more preferably, 10.8 to 11.8wt %.

Mo is added to improve the high temperature strength. In the steelcontaining W in an amount of more than 1 wt % like the inventive steel,however, the addition of Mo in an amount of 0.5 wt % or more reduces thetoughness and the fatigue strength. The content of Mo is thus limited ina range of 0.5 wt % or less, preferably, 0.05 to 0.45 wt %, morepreferably, 0.1 to 0.2 wt %.

W is an element of suppressing aggregation/coarsening of carbides andpromoting solid-solution of a matrix, and therefore, W is effective tosignificantly increase the long time strength at a high temperature of620° C. or more. The content of W is preferably in a range of 1 to 1.5wt % for the alloy used at 620° C.; in a range of 1.6 to 2.0 wt % forthe alloy used at 630° C.; in a range of 2.1 to 2.5 wt % for the alloyused at 640° C.; in a range of 2.6 to 3.0 wt % for the alloy used at650° C.; and in a range of 3.1 to 3.5 wt % for the alloy used at 660° C.The addition of W in an amount of 3.5 wt % or more may cause occurrenceof δ ferrit, leading to reduction in toughness. The content of W is thuslimited in a range of 1 to 3.5 wt %, preferably, 2.4 to 3.0 wt %, morepreferably, 2.5 to 2.7 wt %.

V is effective to increase the creep rupture strength by precipitating acarbo-nitride of V. The effect cannot be sufficiently achieved byaddition of V in an amount of less than 0.05 wt %. The addition of V inan amount of more than 0.3 wt % may cause occurrence of δ ferrit,leading to reduction in fatigue strength. The content of V is preferablyin a range of 0.10 to 0.25 wt %, more preferably, 0.15 to 0.23 wt %.

Nb is very effective to increase the high temperature strength byprecipitating a carbide (NbC); however, the addition of Nb in anexcessively large amount causes a coarsened eutectic carbide,particularly, in the case of a large-sized ingot, causing precipitationof δ ferrite which reduces the high temperature strength and fatiguestrength. In this regard, the content of Nb is limited in a range of0.20 wt % or less. Meanwhile, when the content of Nb is less than 0.01wt %, the effect cannot be sufficiently achieved. In particular, thecontent of Nb may be in a range of 0.02 to 0.15 wt %, preferably, 0.04to 0.10 wt %.

Co is an important element which is a factor distinguishing theinventive material from the conventional material. According to thepresent invention, the addition of Co is effective to significantlyimprove the high temperature strength as well as the toughness. This isdue to interaction with addition of W, and is a phenomenon inherent tothe inventive alloy containing W in an amount of 1 wt % or more. Torealize the addition effect of Co, the lower limit of Co in theinventive alloy is set at 2.0 wt %. When Co is added in an excessivelylarge amount, not only the effect is saturated but also the toughness isreduced. The upper limit of Co is set at 10 wt %. The content of Co ispreferably in a range of 2 to 3 wt % for the alloy used at 620° C.; 3.5to 4.5 wt % for the alloy used at 630° C.; 5 to 6 wt % for the alloyused at 640° C.; 6.5 to 7.5 wt % for the alloy used at 650° C.; and 8 to9 wt % for the alloy used at 660° C.

N is also an important element which is another factor distinguishingthe inventive material from the conventional material. N is effective toimprove the creep rupture strength and prevent occurrence of the δferrite structure. When the content of N is 0.01 wt % or less, theeffect cannot be sufficiently achieved, while when it is more than 0.05wt %, the toughness is reduced and also the creep rupture strength islowered. In particular, the content of N may be in a range of 0.01 to0.03 wt %, preferably, 0.015 to 0.025 wt %.

B is effective to increase the high temperature strength by a functionof strengthening crystal boundaries and a function of blockingaggregation/coarsening of a M23C6 type carbide because B is dissolved inthe M23C6 type carbide in the solid state. To achieve the effect, B ismust be added in an amount of 0.001 wt % or more; however, the additionof B in an amount more than 0.03 wt % exerts adverse effect onweldability and forging ability. The content of B is limited in a rangeof 0.001 to 0.03 wt %, preferably, 0.001 to 0.01 wt %, more preferably,0.01 to 0.02 wt %.

Ta, Ti and Zr are effective to increase the toughness. To achieve theeffect, 0.15 wt % or less of Ta, 0.1 wt % or less of Ti, and 0.1 wt % orless of Zr may be added singly or in combination. In the case of theaddition of Ta in an amount of 0.1 wt % or more, the addition of Nb canbe omitted.

The rotor shaft, at least the first stage rotating blade, and at leastthe first stage stationary blade according to the present invention,which are operated at a steam temperature of 620 to 630° C., arepreferably made from a full temper martensite steel containing 0.09 to0.20 wt % of C, 0.15 wt % or less of Si, 0.05 to 1.0 wt % of Mn, 9.5 to12.5 wt % of Cr, 0.1 to 1.0 wt % of Ni, 0.05 to 0.30 wt % of V, 0.01 to0.06 wt % of N, 0.05 to 0.5 wt % of Mo, 2 to 3.5 wt % of W, 2 to 4.5 wt% of Co, and 0.001 to 0.030 wt % of B, the balance being 77 wt % or moreof Fe. The rotor shaft and the like, which are operated at a temperatureof 635 to 660° C., are preferably made from a full temper martensitesteel having the same composition as described above except that thecontent of Co is set in a range of 5 to 8 wt % and the balance is set at78 wt % or more of Fe. Further, the rotor shaft and the like, which areoperated at a temperature of 620 to 660° C., are preferably made from asteel having the same composition as described above except that thecontent of Mn is reduced to a value in a range of 0.03 to 0.2 wt % andthe content of B is reduced to a value in a range of 0.001 to 0.01 wt %for increasing the strength. In particular, a steel suitable to be usedat a temperature of 630° C. or less and a steel suitable to be used at atemperature of 630 to 660° C. are preferably obtained by addition of 2to 4 wt % of Co and 0.001 to 0.01 wt % of B, and addition of 5.5 to 9.0wt % of Co, and 0.01 to 0.03 wt % of B to a basic composition containing0.09 to 0.20 wt % of C, 0.1 to 0.7 wt % of Mn, 0.1 to 1.0 wt % of Ni,0.10 to 0.30 wt % of V, 0.02 to 0.05 wt % of N, 0.05 to 0.5 wt % of Mo,2 to 3.5 wt % of W, respectively.

For the rotor shaft or the like, the Cr equivalent calculated by theequation to be described later is preferably in a range of 4 to 10.5,more preferably, 6.5 to 9.5.

The rotor material used for each of the high pressure turbine and theintermediate pressure turbine of the steam turbine of the presentinvention preferably has a uniform temper martensite structure becausethe presence of a δ ferrite structure reduces the fatigue strength andthe toughness. To obtain the temper martensite structure, it is requiredto set the Cr equivalent calculated by the above equation in a range of10 or less by adjusting the composition. When the Cr equivalent isexcessively low, the creep rupture strength is reduced. The Crequivalent is limited in a range of 4 or more. In particular, the Crequivalent is preferably in a range of 5 to 8.

The steam turbine rotor, operable in steam at a temperature of 620° C.or more, of the present invention is produced in the followingprocedure. A raw material having a specific composition is melted in anelectric furnace, followed by carbon/vacuum deoxidation, and cast in ametal mold to form an ingot. The ingot is then forged to prepare anelectrode bar. The electrode bar is melted by an electroslag re-meltingprocess to form an ingot, and the ingot is forged into a rotor shape.The forging must be performed at a temperature of 1150° C. or less forpreventing occurrence of forging crack. The forged steel is annealed,and is subjected to quenching (quenching temperature: 1000 to 1100° C.)and to double temper (temper temperature: 550 to 650° C., 670 to 770°C.).

Each of the blade, nozzle, inner casing fastening bolt, intermediatepressure portion first stage diaphragm according to the presentinvention is vacuum-melted and is cast in a die in vacuum to prepare aningot. The ingot is hot-forged at the same temperature as describedabove into a specific shape. The forged steel is heated at a temperatureof 1050 to 1150° C. and water-quenched or oil-quenched, followed bytemper at a temperature of 700 to 800° C., and is machined into a bladehaving a specific shape. The vacuum melting is performed under a vacuumof 10⁻¹ to 10⁻⁴ mm Hg. The heat resisting steel of the present inventioncan be used for all stages of blades and nozzles of each of the highpressure portion and the intermediate pressure portion, andparticularly, the steel is required to be used for the first stage bladeand nozzle.

(3) There will be described the composition of a material used for arotor shaft of each of the high pressure turbine, intermediate pressureturbine or high pressure/intermediate pressure integral type turbine ofthe steam turbine of the present invention, which is operable at atemperature of 600 to less than 620° C.

C is required to be added in an amount of 0.05 wt % or more forincreasing the tensile strength; however, when the content of C is morethan 0.25 wt %, the structure becomes unstable when the alloy is exposedto a high temperature atmosphere for a long time, leading to reductionin long time creep rupture strength. The content of C is limited in arange of 0.05 to 0.25 wt %, preferably, 0.1 to 0.2 wt %.

Nb is very effective to increase the high temperature strength. However,the addition of Nb in an excessively large amount precipitates acorsened carbide of Nb, particularly, for a large-sized ingot; reducesthe concentration of C in the matrix, resulting in the reduced strength;and precipitate δ ferrite which reduces the fatigue strength. Thecontent of Nb must be limited in a range of 0.15 wt % or less.Meanwhile, when the content of Nb is less than 0.02 wt %, the effectcannot be sufficiently achieved. The content of Nb is preferably in arange of 0.07 to 0.12 wt %.

N is effective to improve the creep rupture strength and preventgeneration of δ ferrite. When the content of N is less than 0.025 wt %,the effect cannot be sufficiently achieved. When it is more than 0.1 wt%, the toughness is significantly reduced. The content of N ispreferably in a range of 0.04 to 0.07 wt %.

Cr is effective to increase the high temperature strength. However, theaddition of Cr in an amount more than 13 wt % causes occurrence of δferrite, and the addition of Cr in an amount of less than 8 wt % makespoor the corrosion resistance against high temperature/high pressuresteam. The content of Cr is preferably in a range of 10 to 11.5 wt %.

V is effective to increase the creep rupture strength. When the contentof V is less than 0.02 wt %, the effect cannot be sufficiently achieved,while when it is more than 0.5 wt %, there occurs δ ferrite whichreduces the fatigue strength. The content of V is preferably in a rangeof 0.1 to 0.3 wt %.

Mo is effective to improve the creep strength by a function ofreinforcement of solid-solution and precipitation hardening. When thecontent of Mo is less than 0.5 wt %, the effect cannot be sufficientlyachieved, while when it is more than 2 wt %, there occurs δ ferritewhich reduces the toughness and creep rupture strength. In particular,the content of Mo is preferably in a range of 0.75 to 1.5 wt %.

Ni is very effective to increase the toughness and prevent occurrence ofδ ferrite. However, the addition of Ni in an amount more than 1.5 wt %undesirably reduces the creep rupture strength. The content of Ni ispreferably in a range of 0.4 to 1 wt %.

Mn is added as a deoxidizer. The effect can be achieved by the additionof a small amount of Mn. The addition of Mn in a large amount more than1.5 wt % reduces the creep rupture strength. The content of Mn ispreferably in a range of 0.5 to 1 wt %.

Si is also added as a deoxidizer. However, in the case of adopting asteel-making technique such as vacuum/carbon deoxidation, thedeoxidization by Si becomes unnecessary. The reduction in the content ofSi is effective to prevent precipitation of δ ferrite and improve thetoughness. For this reason, the content of Si must be limited in a rangeof 0.6 wt % or less. If it is added, the content of Si is preferably setat 0.25 wt %.

W is an element capable of significantly increasing the high temperaturestrength in a slight amount. When the content of W in an amount lessthen 0.1 wt %, the effect is small, while when it is more than 0.65 wt%, the strength is rapidly reduced. The content of W should be in arange of 0.1 to 0.65 wt % or less. On the other hand, when the contentof W in an amount more than 0.5 wt %, the toughness is significantlyreduced. For a member requiring the toughness, the content of W may beset at a value less than 0.5 wt %. The content of W is preferably in arange of 0.2 to 0.45 wt %.

Al is an effective element as a deoxidizer. The content of Al may be setat 0.02 wt % or less. The addition of Al in an amount more than 0.02 wt% reduces the high temperature strength.

(4) As for the rotor shaft of the steam turbine, made from the 12% Crbased martensite steel according to the present invention, builduplayers having a high bearing characteristic are preferably formed bywelding on the surface of a base material for forming a jounal portionof the rotor shaft. To be more specific, three to ten buildup layers maybe formed by welding using a welding material made from a steel. In thiscase, the first, second, third, and fourth layers are built up bywelding using welding materials of which the Cr contents aresequentially lowered, and the fifth layer and the later layers are builtup by welding using welding materials of which the Cr contents areidentical to each other. Further, the Cr content of the welding materialused for welding of the first layer is smaller 2 to 6 wt % than that ofthe base material, and the Cr content of each of the fourth layer andthe later layers is set at 0.5 to 3 wt % (preferably, 1 to 2.5 wt %).

In the present invention, to improve the bearing characteristic of thejounal portion, buildup welding is preferable in terms of high safety.The buildup welding, however, may replaced with shrinkage fit orinsertion of a sleeve made from a low alloy steel containing Cr in anamount of 1 to 3 wt %.

To gradually change the content of Cr in buildup layers, it is desiredto provide three layers or more; however, if ten layers or more areprovided, the effect is saturated. The total thickness of the builduplayers is represented by about 18 mm after final finishing. To ensuresuch a total thickness, it is desired to provide at least five builduplayers excluding a cutting allowance for final finishing. Each of thethird layer and the later layers preferably has a martensite structurein which a carbide is precipitated. In particular, the welding layer ofeach of the fourth layer and the later layers preferably contains 0.01to 0.1 wt % of C, 0.3 to 1 wt % of Si, 0.3 to 1.5 wt % of Mn, 0.5 to 3wt % of Cr, and 0.1 to 1.5 wt % of Mo, the balance being Fe.

(5) There will be described a reason for limiting the content of eachcomponent of the ferrite based heat resisting steel used for an innercasing governor valve box, combination re-heat valve box, main steamlead pipe, main steam inlet pipe, re-heat inlet pipe, high pressureturbine nozzle box, intermediate pressure turbine first stage diaphragm,high pressure turbine main steam inlet flange, elbow, and main steamstop valve of each of the high pressure turbine, intermediate pressureturbine, and high pressure/intermediate pressure turbine.

By adjusting the Ni/W ratio in a range of 0.25 to 0.75, the ferritebased heat resisting cast steel as the casing material satisfiescharacteristics required for the high pressure and intermediate pressureinner casings, main steam stop valve and governor valve casing of anultrasuper critical pressure turbine operated at 621° C. and 250 kgf/cm²or more, that is, exhibits a 10⁵ h creep rupture strength (at 625° C.)of 9 kgf/mm² or more and an impact absorption energy (at roomtemperature) of 1 kgf-m or more.

In the ferrite based heat resisting cast steel as the casing materialaccording to the present invention, to obtain a high temperaturestrength, a low temperature toughness, and a high fatigue strength, itis desired to adjust the composition such that the Cr equivalentcalculated by the above equation is in a range of 4 to 10.

The 12% Cr based heat resisting steel of the present invention, which isoperated in steam at a temperature of 621° C. or more, must exhibit a10⁵ h creep rupture strength (at 625° C.) of 9 kgf/mm² or more and animpact absorption energy (at room temperature) of 1 kgf-m or more, andto ensure a higher reliability, it preferably exhibits a 10⁵ h creeprupture strength (at 625° C.) of 10 kgf/mm² or more and an impactabsorption energy (at room temperature) of 2 kgf-m or more.

C is required to be added in an amount of 0.06 wt % or more forincreasing the tensile strength. When the content of C is more than 0.16wt %, the metal structure becomes unstable when the alloy is exposed toa high temperature atmosphere for a long time, leading to reduction inlong time creep rupture strength. The content of C is limited in a rangeof 0.06 to 0.16 wt %, preferably, 0.09 to 0.14 wt %.

N is effective to improve the creep rupture strength and preventoccurrence of a δ ferrite. When the content of N is less than 0.01 wt %,the effect cannot be sufficiently achieved, while when it is more than0.1 wt %, the effect is already saturated, and the toughness is reducedand the creep rupture strength is lowered. The content of N ispreferably in a range of 0.02 to 0.06 wt %.

Mn is added as a deoxidizer. The effect can be achieved by the additionof a small amount of Mn. The addition of Mn in an amount more than 1 wt% reduces the creep rupture strength. The content of Mn is preferably ina range of 0.4 to 0.7 wt %.

Si is also added as a deoxidizer. However, in the case of adopting asteel-making technique such as vacuum/carbon deoxidation, thedeoxidization by Si becomes unnecessary. The reduction in content of Siis effective to prevent occurrence of a undesirable δ ferrite structure.If Si is added, the content of Si must be limited in a range of 0.5 wt %or less, preferably, 0.1 to 0.4 wt %.

V is effective to increase the creep rupture strength. When the contentof V is less then 0.05 wt %, the effect cannot be sufficiently achieved,while when it is more than 0.35 wt %, there occurs δ ferrite whichreduces fatigue strength. The content of V is preferably in a range of0.15 to 0.25 wt %.

Nb is very effective to increase the high temperature strength. However,the addition of Nb in an excessively large amount causes a coarsenedeutectic carbide of Nb, particularly, in the case of a large-sizedingot, to rather reduce the strength and precipitate δ ferrite whichreduces the fatigue strength. The content of Nb is limited in a range of0.15 wt % or less. When the content of Nb is less than 0.01 wt %, theeffect cannot be sufficiently achieved. In the case of a large-sizedingot, particularly, the content of Nb may be in a range of 0.02 to 0.1wt %, preferably, 0.04 to 0.08 wt %.

Ni is very effective to increase the toughness and prevent occurrence ofδ ferrite. When the content of Ni is less than 0.2 wt %, the effectcannot be sufficiently achieved, while when it is more than 1.0 wt %,the creep rupture strength is undesirably reduced. The content of Ni ispreferably in a range of 0.4 to 0.8 wt %.

Cr is effective to improve the high temperature strength and hightemperature oxidation. When the content of Cr is more than 12 wt %,there occurs a undesirable δ ferrite structure, while when it is lessthan 8 wt %, the oxidation resistance against high temperature/highpressure steam becomes insufficient. The addition of Cr is effective toincrease the creep rupture strength; however, excessively large amountof Cr causes a undesirable δ ferrite structure and reduces thetoughness. The content of Cr is preferably in a range of 8.0 to 10 wt %,more preferably, in a range of 8.5 to 9.5 wt %.

W is effective to significantly increase the high temperature/long timestrength. When the content of W is less than 1 wt %, the effect becomesinsufficient if the heat resisting steel is used at a temperature of 620to 660° C., while when it is more than 4 wt %, the toughness is reduced.The content of W is preferably in a range of 1.0 to 1.5 wt % for thealloy used at 620° C.; in a range of 1.6 to 2.0 wt % for the alloy usedat 630° C.; in a range of 2.1 to 2.5 wt % for the alloy used at 640° C.;in a range of 2.6 to 3.0 wt % for the alloy used at 650° C.; and in arange of 3.1 to 3.5 wt % for the alloy used at 660° C.

W has interaction with Ni, and both the strength and toughness can beincreased by setting the ratio Ni/W in a range of 0.25 to 0.75.

Mo is effective to increase the high temperature strength. However, forthe alloy containing w in an amount more than 1 wt % like the cast steelof the present invention, the addition of Mo in an amount of 1.5 wt % ormore reduces the toughness and fatigue strength. The content of Mo to beadded is limited in the range of 1.5 wt % or less, preferably, 0.4 to0.8 wt %, more preferably, 0.55 to 0.70 wt %.

Ta, Ti and Zr are effective to increase the toughness. To achieve theeffect, 0.15 wt % or less of Ta, 0.1 wt % or less of Ti, and 0.1 wt % orless of Zr may be added singly or in combination. In the case of theaddition of Ta in an amount of 0.1 wt % or more, the addition of Nb canbe omitted.

The heat resisting cast steel as the casing material of the presentinvention preferably has a uniform temper martensite structure becausethe presence of a δ ferrite structure reduces the fatigue strength andthe toughness. To obtain the temper martensite structure, it is requiredto set the Cr equivalent calculated by the above equation in a range of10 or less by adjusting the composition. When the Cr equivalent isexcessively low, the creep rupture strength is reduced. The Crequivalent is limited in a range of 4 or more. In particular, the Crequivalent is preferably in a range of 6 to 9.

B is effective to significantly increase the creep rupture strength athigh temperatures (620° C. or more). The addition of B in an amount morethan 0.003 wt % degrades weldability, and therefore, the upper limit ofthe content of B is set at 0.003 wt %. In the case of the alloy used fora large-sized casing, the upper limit of the content of B may be set at0.0028 wt %. The content of B is preferably in a range of 0.0005 to0.0025 wt %, more preferably, 0.001 to 0.002 wt %.

The casing, which covers high pressure steams at a temperature of 620°C. or more, is applied with a high stress due to an inner pressure.Accordingly, to prevent occurrence of creep rupture, the casing isrequired to exhibit a 10⁵ h creep rupture strength of 10 kgf/mm² ormore. Further, since the casing is applied with a thermal stress whenthe metal temperature is low upon starting, it must exhibit an impactabsorption energy (at room temperature) of 1 kgf-m or ore for preventingoccurrence of brittle fracture. For the casing material used on thehigher temperature side, its strength can be increased by addition of Coin an amount of 10 wt % or less. To be specific, the content of Co ispreferably in a range of 1 to 2 wt % for the alloy used at 620° C.; in arange of 2.5 to 3.5 wt % for the alloy used at 630° C.; in a range of 4to 5 wt % for the alloy used at 640° C.; in a range of 5.5 to 6.5 wt %for the alloy used at 650° C.; and in a range of 7 to 8 wt % for thealloy used at 660° C. For the alloy used at a temperature of 600 to 620°C., Co may be not added.

To produce a casing material with less defects, a large-size ingothaving a weight of about 50 ton must be prepared, which requires a highlevel steel-making technique. The heat resisting cast steel as thecasing material of the present invention is produced by melting a rawmaterial having a specific composition in an electric furnace, followedby ladle refining, and casting molten steel in a sand mold. In thiscase, a high quality ingot with less casting defects such as shrinkagecavities can be obtained by sufficiently refining and deoxidizing moltensteel before casting.

The above cast steel is annealed at a temperature of 1000 to 1150° C.,and heated at a temperature of 1000 to 1100° C. and rapidly cooled(normalizing), followed by double temper (550 to 750° C., 670 to 770°C.), to obtain a steam turbine casing operable in steam at a temperatureof 621° C. or more. When each of the annealing temperature andnormalizing temperature is less than 1000° C., a carbonitride cannot besufficiently dissolved in the solid-state, while when it is excessivelyhigh, there may occur coarsening of crystal grains. The double temperperfectly decomposes retained austenite to form a uniform tempermartensite. In accordance with the above process, there can be produceda steam turbine casing having a 10⁵ h creep rupture strength (at 625°C.) of 10 kgf/mm² or more and an impact absorption energy (at roomtemperature) of 1 kgf-m or more. Such a casing is operable in steam at atemperature of 620° C. or more.

When the content of O is more than 0.015 wt %, the high temperaturestrength and the toughness are reduced, and therefore, the content of Ois limited in a range of 0.015 wt % or less, preferably, 0.010 wt % orless.

For the casing material of the present invention, the Cr equivalent isset at the same value as described above to reduce the δ ferrite amountto a value of 5 wt % or less. The δ ferrite amount is preferably reducedto zero.

While the inner casing is made from a cast steel, the other parts arepreferably made from forged steels.

(6) Others

(A) The rotor shaft for the low pressure steam turbine is preferablymade from a low alloy steel which contains 0.2 to 0.3 wt % of C, 0.1 wt% or less of Si, 0.2 wt % or less of Mn, 3.2 to 4.0 wt % of Ni, 1.25 to2.25 wt % of Cr, 0.1 to 0.6 wt % of Mo, and 0.05 to 0.25 wt % of V, andwhich has a full temper bainite structure. This rotor shaft ispreferably produced in the same manner as that for the above rotor shaftof the high pressure or intermediate pressure steam turbine. Inparticular, the rotor shaft is preferably produced by a super cleanprocess using a raw material in which the amount of Si is reduced to avalue of 0.05 wt % or less, the amount of Mn is reduced to a value of0.1 wt % or less, and the total amount of other impurities such as P, S,As, Sb and Sn is reduced as much as possible, for example, to a value0.025 wt % or less. In this case, the amount of each of P and S ispreferably in a range of 0.010 wt % or less; the amount of each of Snand As is preferably in a range of 0.005 wt % or less; and the amount ofSb is preferably in a range of 0.001 wt % or less.

(B) The final stage blade and nozzle for the low pressure turbine ispreferably made form a full temper martensite steel containing 0.05 to0.2 wt % of C, 0.1 to 0.5 wt % of Si, 0.2 to 1.0 wt % of Mn, 10 to 13 wt% of Cr, and 0.04 to 0.2 wt % of Cr.

(C) The inner casing and outer casing for the low pressure turbine arepreferably made from a carbon cast steel containing 0.2 to 0.3 wt % ofC, 0.3 to 0.7 wt % of Si, and 1 wt % of Mn.

(D) The main steam stop valve casing and steam governor valve casing arepreferably made from a full temper martensite steel containing 0.1 to0.2 wt % of C, 0.1 to 0.4 wt % of Si, 0.2 to 1.0 wt % of Mn, 8.5 to 10.5wt % of Cr, 0.3 to 1.0 wt % of Mo, 1.0 to 3.0 wt % of W, 0.1 to 0.3 wt %of V, 0.03 to 0.1 wt % of Nb, 0.03 to 0.08 wt % of N, and 0.0005 to0.003 wt % of B.

(E) As the final stage rotating blade for the low pressure turbine,there may be used a Ti alloy in place of the 12% Cr based steel. Inparticular, the final stage rotating blade having a length of 40 inchesor more is made from a Ti alloy containing 5 to 8 wt % of Al and 3 to 6wt % of V; the blade having a length of 43 inches is made from a highstrength Ti alloy containing 5.5 to 6.5 wt % of Al and 3.5 to 4.5 wt %of V; and the blade having a length of 46 inches is made from a higherTi alloy containing 4 to 7 wt % of Al, 4 to 7 wt % of V and 1 to 3 wt %of Sn.

(F) The outer casing for each of the high pressure turbine, intermediatepressure turbine and high pressure/intermediate pressure turbine is madefrom a cast steel which contains 0.10 to 0.20 wt % of C, 0.05 to 0.6 wt% of Si, 0.1 to 1.0 wt % of Mn, 0.1 to 0.5 wt % of Ni, 1 to 2.5 wt % ofCr, 0.5 to 1.5 wt % of Mo, and 0.1 to 0.35 wt % of V, and preferably, atleast one of 0.025 wt % or less of Al, 0.0005 to 0.004 wt % of B, and0.05 to 0.2 wt % of Ti, and which has a full temper bainite structure.In particular, there is preferably used a cast steel containing 0.10 to0.18 wt % of C, 0.20 to 0.60 wt % of Si, 0.20 to 0.50 wt % of Mn, 0.1 to0.5 wt % of Ni, 1.0 to 1.5 wt % of Cr, 0.9 to 1.2 wt % of Mo, 0.2 to 0.3wt % of V, 0.001 to 0.005 wt % of Al, 0.045 to 0.10 wt % of Ti, and0.0005 to 0.0020 wt % of B. In this composition, more preferably, theTi/Al ratio is in a range of 0.5 to 10.

(G) The first stage blade for each of the high pressure turbine,intermediate pressure turbine, and high pressure/intermediate pressureturbine (high pressure side and the intermediate pressure side) at asteam temperature of 625 to 650° C. is made from a Ni based alloycontaining 0.03 to 0.20 wt % (preferably, 0.03 to 0.15 wt %), 12 to 20wt % of Cr, 9 to 20 wt % of Mo (preferably, 12 to 20 wt %), 12 wt % orless of Co (preferably, 5 to 12 wt %), 0.5 to 1.5 wt % of Al, 1 to 3 wt% of Ti, 5 wt % or less of Fe, 0.3 wt % or less of Si, 0.2 wt % or lessof Mn, 0.003 to 0.015 wt % of B, and one kind or more of 0.1 wt % orless of Mg, 0.5 wt % or less of a rare earth element and 0.5 wt % orless of Zr. In addition, the wording "or less" contains 0 wt %. Theabove alloy is forged, followed by solution treatment, and subjected toageing treatment at a temperature of 700 to 870° C.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a relationship between a tensile strengthand a (Ni--Mo) amount (wt %);

FIG. 2 is a diagram showing a relationship between an impact value and a(Ni--Mo) amount (wt %);

FIG. 3 is a diagram showing a relationship between a tensile strengthand a quenching temperature;

FIG. 4 is a diagram showing a relationship between a tensile strengthand a temper temperature;

FIG. 5 is a diagram showing a relationship between an impact value and aquenching temperature;

FIG. 6 is a diagram showing a relationship between an impact value and atemper temperature;

FIG. 7 is a diagram showing a relationship between an impact value and atensile strength;

FIG. 8 is a sectional view of a high pressure steam turbine and anintermediate pressure steam turbine, which are connected to each other,according to the present invention;

FIG. 9 is a sectional configuration view of a low pressure steam turbineaccording to the present invention;

FIG. 10 is a perspective view of a turbine rotating blade according tothe present invention;

FIG. 11 is a sectional view of a high pressure/intermediate pressuresteam turbine according to the present invention;

FIG. 12 is a sectional view of a rotor shaft for the highpressure/intermediate pressure steam turbine according to the presentinvention;

FIG. 13 is a sectional view of a low pressure steam turbine according tothe present invention;

FIG. 14 is a sectional view of a rotor shaft for the low pressure steamturbine according to the present invention; and

FIG. 15 is a perspective view of a leading end portion of a turbinerotating blade according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1]

Table 1 shows chemical compositions (wt %) of 12% Cr based steels usedas long blades materials for steam turbines. Each sample of 150 kg wasmelted by a vacuum arc melting process, being heated to a temperatureless than 1150° C., and forged, to prepare an experimental material.Sample No. 1 was heated at 1000° C. for one hour and cooled to roomtemperature by oil quenching, and then heated to and kept at 570° C. fortwo hours and air-cooled. Sample No. 2 was heated at 1050° C. for onehour and cooled to room temperature by oil quenching, and then heated toand kept at 570° C. for two hours and air-cooled. Each of Sample Nos. 3to 6 was heated at 1050° C. for one hour and cooled to room temperatureby oil quenching, and then heated to and kept at 560° C. for two hoursand air-cooled (primary temper), and further heated to and kept at 580°C. for two hours and furnace-cooled (secondary temper).

In Table 1, Sample Nos. 3, 4 and 5 are inventive materials; Sample No. 6is a comparative material; and Sample Nos. 1 and 2 are existing longblade materials.

Table 2 shows mechanical properties of these samples at roomtemperature. From the results shown in Table 2, it is revealed that eachof the inventive materials (Sample Nos. 3 to 5) sufficiently satisfies atensile strength (120 kgf/mm² or more, or 128.5 kgf/mm² or more) and alow temperature toughness (Charpy V-notch impact value (at 20° C.): 2.5kgf-m/cm² or more) which are required for a long blade material for asteam turbine.

On the contrary, each of Sample Nos. 1 and 6 as the comparativematerials exhibits a tensile strength and an impact value which arelower than those required for a long blade for a steam turbine. SampleNo. 2 as the comparative material is low in tensile strength andtoughness. Sample No. 5 exhibits an impact value of 3.8 kgf-m/cm² whichis slightly lower than a value of 4 kgf-m/cm² or more required for along blade of 43 inches or more.

                                      TABLE 1                                     __________________________________________________________________________                                         Nb     Nb                                                                     --     --                                No.                                                                              C  Si Mn Cr Ni Mo W  V  Nb N  Ni-Mo                                                                             C  C + Nb                                                                            N                                 __________________________________________________________________________    1  0.12                                                                             0.15                                                                             0.75                                                                             11.5                                                                             2.60                                                                             1.70                                                                             -- 0.36                                                                             -- 0.03                                                                             0.90                                                                              -- --  --                                2  0.28                                                                             0.28                                                                             0.71                                                                             11.6                                                                             0.73                                                                             1.10                                                                             1.12                                                                             0.21                                                                             -- 0.04                                                                             --  -- --  --                                3  0.14                                                                             0.04                                                                             0.16                                                                             11.4                                                                             2.70                                                                             2.10                                                                             -- 0.26                                                                             0.08                                                                             0.06                                                                             0.60                                                                              0.57                                                                             0.22                                                                              1.33                              4  0.13                                                                             0.04                                                                             0.15                                                                             11.5                                                                             2.50                                                                             2.40                                                                             -- 0.28                                                                             0.10                                                                             0.05                                                                             0.10                                                                              0.77                                                                             0.23                                                                              2.0                               5  0.13                                                                             0.06                                                                             0.15                                                                             11.4                                                                             2.65                                                                             3.10                                                                             -- 0.25                                                                             0.11                                                                             0.06                                                                             -0.45                                                                             0.85                                                                             0.22                                                                              1.83                              6  0.14                                                                             0.04                                                                             0.17                                                                             11.4                                                                             2.61                                                                             3.40                                                                             -- 0.26                                                                             0.10                                                                             0.06                                                                             -0.79                                                                             0.71                                                                             0.24                                                                              1.67                              7  0.14                                                                             0.04                                                                             0.15                                                                             11.5                                                                             2.60                                                                             2.30                                                                             -- 0.27                                                                             0.10                                                                             0.07                                                                             0.30                                                                              0.71                                                                             0.24                                                                              1.43                              __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                                Tensile             Reduction                                                                            Impact                                     Sample  strength Elongation of area                                                                              value                                      No.     (kgf/mm.sup.2)                                                                         (%)        (%)    (kgf-m/cm.sup.2)                           ______________________________________                                        1       114.4    19.0       60.1   8.0                                        2       114.6    18.6       59.7   1.2                                        3       132.5    21.0       67.1   5.2                                        4       134.9    20.8       66.8   4.8                                        5       137.0    18.5       59.8   3.8                                        6       118.7    21.1       67.3   5.2                                        7       133.5    20.1       60.4   5.1                                        ______________________________________                                    

FIG. 1 is a diagram showing a relationship between a (Ni--Mo) amount anda tensile strength. In this embodiment, both a strength and toughness ata low temperature are improved by adjusting the contents of Ni and Mo tobe substantially equal to each other. As a difference between thecontents of Ni and Mo becomes larger, the strength becomes lower. Asshown in FIG. 1, when the Ni content is smaller, 0.6% or more, than theMo content, the strength is rapidly lowered. On the contrary, when theNi content is larger, 1.0% or more, than the Mo content, the strength isalso rapidly lowered. As a result, the (Ni--Mo) amount suitable forenhancing the strength is in a range of -0.6% to 1.0%.

FIG. 2 is a diagram showing a relationship between a (Ni--Mo) amount andan impact value. As shown in the figure, the impact value is low near-0.5% of the (Ni--Mo) amount, and is high in regions less than -0.5% andmore than 0.5% of the (Ni--Mo) amount.

FIGS. 4 to 6 are diagrams showing dependences of heat-treatmentconditions (quenching temperature and secondary temper temperature) onthe tensile strength and impact value for Sample No. 3. The quenchingtemperature is in a range of 975 to 1125° C., and the primary tempertemperature is in a range of 550 to 560° C. and the secondary tempertemperature is in a range of 560 to 590° C. From the results shown inthe figures, it is confirmed that Sample No. 3, which is heat-treated inthe above heat-treatment conditions, satisfies characteristics requiredas a long blade material (tensile strength≧128.5 kgf/mm², Charpy V-notchimpact value (at 20° C.)≧4 kgf-m/cm²). In addition, the secondary tempertemperature in FIGS. 3 and 5 is 575° C., and the quenching temperaturein each of FIGS. 4 and 6 is 1050° C.

FIG. 7 is a diagram showing a relationship between a tensile strengthand an impact value. The 12% Cr based steel in this embodiment is, asdescribed above, preferred to exhibit a tensile strength of 120 kgf/mm²or more and an impact value of 4 kgf-m/cm² or more, and is morepreferred to exhibit an impact value (y) which is not less than a valueobtained by an equation of [-0.45×(tensile strength)+61.5].

The 12% Cr based steel according to the present invention is preferredto have such a composition that the (C+Nb) amount is in a range of 0.18to 0.35%; the (Nb/C) ratio is in a range of 0.45 to 1.00; and the (Nb/N)ratio is in a range of 0.8 to 3.0.

[Embodiment 2]

With a sudden rise in cost of fuel after oil crisis as a turning-point,a boiler of a type of direct combustion of pulverized coal at a steamtemperature of 600 to 649° C. and a steam turbine have been required tobe used for the purpose of improving a thermal efficiency by settinghigh the steam conditions. One example of the boiler used under suchhigh steam conditions is shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Plant output       1050 MW                                                    Operating type     Constant pressure type                                     ______________________________________                                        Specifi- Type          Radiative reheat type                                  cation                 ultrasuper critical                                    of                     pressure once-through                                  boiler                 boiler                                                          Amount of     3170 t/h                                                        evaporation                                                                   Steam pressure                                                                              24.12 Mpa[G]                                                    Steam temperature                                                                           630° C./630° C.                          Perform- Combustion                                                           ance     characteristic                                                                NOx           120 ppm                                                         Unburned com- 3.2%                                                            bustible in ash                                                               Rate of change in                                                                           4%/min                                                          load                                                                          (50 ←→ 100%)                                                      Minimum load  33% ECR (Wet bank coal)                                ______________________________________                                    

With the increased plant output, the size of a pulverized coalcombustion furnace is enlarged. For example, for a plant output of 1050MW class, the furnace has a width of 31 m and a depth of 16 m; and for aplant output of 1400 MW class, the furnace has a width of 34 m and adepth of 18 m.

Table 4 shows a main specification of a steam turbine in which the steamtemperature is set at 625° C. and the plant output is set at 1050 MW.The steam turbine in this embodiment is of a crosscompound/quadruple-flow exhaust type. In this steam turbine, the lengthof a final stage blade in a low pressure turbine is 43 inches. A turbineconfiguration A has a turbine combination of [(HP-IP)+2×LP] and isoperated at the number of revolution of 3000 rpm, and a turbineconfiguration B has a turbine combination of [(HP-LP)+(IP-LP)] and isoperated at the number of revolution of 3000 rpm. Main components in thehigh pressure portion are made from materials shown in Table 4. In thehigh temperature portion (HP), the steam temperature is 625° C. and thesteam pressure is 250 kgf/cm². The steam supplied from the HP portion isheated to 625° C. by a re-heater and is supplied to the intermediatepressure portion (IP). The intermediate pressure portion is operated atthe steam temperature 625° C. and at a steam pressure of 45 to 65kgf/cm². The steam at a steam temperature of 400° C. is supplied in thelow pressure portion (LP), and the steam at a steam temperature of 100°C. or less and in a vacuum of 722 mm Hg is supplied to a steamcondenser.

                                      TABLE 4                                     __________________________________________________________________________    Type of turbine                                                                            CC4F-43                                                          Number of revolution                                                                       3000/3000 RPM                                                    Steam condition                                                                            24.1 Mpa-625° C./625° C.                           Configuration of turbine                                                                 A                                                                                ##STR1##                                                                   B                                                                                ##STR2##                                                        Structure of first stage blade                                                             Double flow type,                                                             2 tenon saddle type dovetail blade                               Final stage blade                                                                          High-strength 12Cr forged steel                                  Main steam stop valve body,                                                                High-strength 12Cr forged steel                                  Steam governor valve body                                                     High pressure rotor                                                                        High-strength 12Cr forged steel                                  Intermediate pressure rotor                                                                High-strength 12Cr forged steel                                  Low pressure rotor                                                                         3.5Ni--Cr--Mo--V forged steel                                    Rotating blade at high                                                                     First stage:                                                     temperature portion                                                                        high-strength 12Cr forged steel                                  High pressure casing                                                          Interior     High-strength 9Cr cast steel                                     Exterior     High-strength Cr--Mo--V--B cast steel                            Intermediate pressure casing                                                  Interior     High-strength 9Cr cast steel                                     Exterior     High-strength Cr--Mo--V--B cast steel                            Gross thermal efficiency                                                                   47.1%                                                            (Rated output, end of                                                         generator)                                                                    __________________________________________________________________________     (CC4F-43: cross compound type quadrupleflow exhaust, 43 inch long blade       HP: high pressure portion, IP: intermediate pressure portion, LP: low         pressure portion, R/H: reheater (boiler))                                

FIG. 8 is a sectional configuration view showing the high pressure steamturbine and the intermediate pressure steam turbine of the turbineconfiguration A shown in Table 4. The high pressure steam turbine has ahigh pressure axle (high pressure rotor shaft) 23 which is disposedinside a high pressure inner casing 18 and a high pressure outer casing19 positioned outside the inner casing 19. High pressure rotating blades16 are planted in the high pressure rotor shaft 23. The above steam at ahigh temperature and a high pressure is produced by the above boiler,passing through a main steam pipe, a flange constituting a main steaminlet portion and an elbow 25, a main steam inlet 28, and is introducedto a first stage double-flow rotating blade from a nozzle box 38. Eightstages of rotating blades are provided on one side of the high pressuresteam turbine, and stationary blades are provided in such a manner as tobe matched with these rotating blades. The rotating blade is of asaddle-dovetail type having double tenons. The length of the first stageblade is about 35 mm. The distance between centers of bearings is about5.8 m. The diameter of the minimum one of portions corresponding to thestationary blades is about 710 mm, and the ratio of the between-bearingdistance to the diameter is about 8.2.

The axial root widths of rotating blade planted portions of the rotorshaft are specified such that the axial root width at the first stage isnearly equal to that of the final stage; and as for the axial rootwidths at the second to eighth stages, the axial root width becomessmaller toward the downstream side stepwise in five steps at the secondstage, third to fifth stages, sixth stage, and seventh and eighthstages. The axial root width of the second stage rotating blade plantedportion is 0.71 times that of the final stage rotating blade plantedportion.

The diameter of a portion, of the rotor shaft, corresponding to thestationary blade is smaller than the diameter of the rotating bladeplanted portion of the rotor shaft. The axial root width of the portion,of the rotor shaft, corresponding to the stationary blade becomessmaller stepwise from that between the second stage and third stagerotating blades to that between the final stage rotating blade and thepreceding one. The latter axial root width is 0.86 times smaller thanthe former axial root width. In some cases, the axial root width of theportion, of the rotor shaft, corresponding to the stationary bladebecomes smaller stepwise in two steps at the second to sixth stages andsixth to ninth stages.

In this embodiment, all of the components other than the first stageblade and the nozzle are made from a 12% Cr based steel not containingW, Co and B. Each of the first stage blade and nozzle is made from amaterial shown in Table 5 (which will be described later). The length ofa blade portion of the rotating blade in this embodiment is in a rangeof 35 to 50 mm at the first stage, and becomes longer in the directionfrom the second stage to the final stage. In particular, depending onthe output of the steam turbine, each of the lengths of the bladeportions of the second to final rotating blades is set in a range of 65to 180 mm; the number of stages is set in a range of 9 to 12; and thelength of the blade portion of the rotating blade on the downstream sidebecomes longer than that of the blade portion of the adjacent rotatingblade on the upstream side at a ratio of 1.10 to 1.15, and the ratiobecomes gradually larger toward the downstream side.

The intermediate pressure steam turbine is operated to rotate agenerator together with the high pressure steam turbine by the steamwhich is discharged from the high pressure steam turbine and heatedagain at 625° C. by a reheater. The intermediate pressure steam turbineis rotated at 3000 rpm. The intermediate pressure turbine hasintermediate pressure inner and outer casings 21 and 22 like the highpressure turbine. Stationary blades are provided correspondingly tointermediate pressure rotating blades 17. Two sets, each being composedof the rotating blades 17 of six stages (first stage: double-flow), areprovided substantially symmetrically right and left in the longitudinaldirection of an intermediate axle (intermediate pressure rotor shaft).The distance between centers of bearings is about 5.8 m. The length ofthe first stage blade is about 100 mm and the length of the final bladeis about 230 mm. The dovetail of each of the first and second stageblades is formed into an inverse-chestnut shape. The diameter of aportion, of the rotor shaft, corresponding to the stationary bladepositioned directly before the final stage rotating blade is about 630mm, and the ratio of the between-bearing distance to this diameter isabout 9.2.

In the intermediate pressure steam turbine in this embodiment, the axialroot width of a rotating blade planted portion of the rotor shaftbecomes larger stepwise in three steps in the order of the first tofourth stages, fifth stage, and final stage. The axial root width of thefinal stage rotating blade planted portion is about 1.4 times largerthan that of the first stage rotating portion planted portion.

In this steam turbine, the diameters of portions, of the rotor shaft,corresponding to stationary blades are set to be small. The axial rootwidth of the portion, of the rotor shaft, corresponding to thestationary blade becomes smaller stepwise in four steps in the order ofthe first stage, second and third stages, and final stage. The axialroot width at the latter stage becomes smaller about 0.75 times thanthat at the latter stage.

In this embodiment, all of the components other than the first stageblade and the nozzle are made from a 12% Cr based steel not containingW, Co and B. Each of the first stage blade and nozzle is made from amaterial shown in Table 5 (which will be described later). The length ofa blade portion of the rotating blade in this embodiment becomes longerin the direction from the first stage to the final stage. In particular,depending on the output of the steam turbine, each of the lengths of theblade portions of the first to final rotating blades is set in a rangeof 60 to 300 mm; the number of stages is set in a range of 6 to 9; andthe length of the blade portion of the rotating blade on the downstreamside becomes longer than that of the blade portion of the adjacentrotating blade on the upstream side at a ratio of 1.1 to 1.2.

The diameter of the rotating blade planted portion is larger than thatof the portion corresponding to the stationary blade. The larger thelength of blade portion of the rotating blade, the larger the width ofthe rotating blade planted portion. The ratio of the width of therotating blade planted portion to the length of the blade portion of therotating blade is in a range of 0.35 to 0.8 and it becomes smallerstepwise in the order from the first stage to the final stage.

FIG. 9 is a sectional view of two low pressure turbines in tandem witheach other, whose structures are substantially identical to each other.Two sets, each being composed of rotating blades 41 of eight stages, aredisposed substantially symmetrically right and left, and stationaryblades 42 are provided correspondingly to the rotating blades 41. Thefinal rotating blade has a length of 43 inches, and is made from the 12%Cr based steel corresponding to Sample No. 7 shown in Table 1. The finalrotating blade is of a double tenon/saddle-dovetail type shown in FIG.10, and a nozzle box 44 is of a double-flow type. A rotor shaft 43 ismade from a super clean forged steel having a full temper bainitestructure. To be more specific, the forged steel contains 3.75 wt % ofNi, 1.75 wt % of Cr, 0.4 wt % of Mo, 0.15 wt % of V, 0.25 wt % of C,0.05 wt % of Si and 0.10 wt % of Mn, the balance being Fe. The rotatingblades other than the final one and the stationary blades are made froma 12% Cr based steel containing 0.1 wt % of Mo. The inner and outercasings are made from a cast steel containing 0.25 wt % of C. In thisembodiment, the distance between centers of bearings 43 is 7500 mm; thediameter of a portion, of the rotor shaft, corresponding to thestationary blade is about 1280 mm; and the diameter of a rotating bladeplanted portion of the rotor shaft is 2275 mm. The ratio of thebetween-bearing distance to the diameter of the portion, of the rotorshaft, corresponding to the stationary blade is about 5.9.

FIG. 10 is a perspective view of a long blade of a size of 1092 mm(43"). Reference numeral 51 indicates a blade portion with which highspeed steam collides; 52 is a portion to be planted in the rotor shaft;53 is a hole into which a pin for supporting the blade applied with acentrifugal force is to be inserted; 54 is an erosion shield (plate madefrom stellite which is a Co-based alloy is joined by welding) forpreventing erosion caused by water drop in steam; and 57 is a cover. Inthis embodiment, the long blade is formed by cutting a one-body forgedpart. It is to be noted that the cover 57 may be mechanically formed ina state being integral with the long blade.

The 43" long blade is produced by melting a material by an electroslagre-melting process, followed by forging and heat-treatment. The forgingwas performed at a temperature in a range of 850 to 1150° C., and theheat-treatment was performed in the condition described in the firstembodiment. Sample No. 7 in Table 1 shows a chemical composition (wt %)of the long blade material. The metal structure of the long bladematerial was a full temper martensite structure.

The tensile strength at room temperature and the Charpy V-notch impactvalue (at 20° C.) of Sample No. 7 are shown in Table 1. It is confirmedthat the 43" long blade exhibits sufficient mechanical properties overthe necessary characteristics, more specifically, a tensile strength of128.5 kgf/mm² or more and a Charpy V-notch impact value (at 20° C.) of 4kgf-m/mm² or more.

In the low pressure turbine in this embodiment, the axial root width ofa rotating blade planted portion of the rotor shaft becomes graduallylarger in four steps in the order of the first to third stages, fourthstage, fifth stage, sixth and seventh stages, and eighth stage. Theaxial root width of the final stage rotating blade planted portionbecomes larger about 6.8 times than that of the first stage rotatingblade planted portion.

The diameters of portions, of the rotor shaft, corresponding tostationary blades are small. The axial root width of the portioncorresponding to the stationary blade becomes gradually larger in threesteps in the order of fifth stage, sixth stage and seventh stage fromthe first stage rotating blade side. The axial root width of the portioncorresponding to the stationary blade on the final stage side becomeslarger about 2.5 times than that of the portion corresponding to thestationary blade between the first and second stage rotating blades.

In this embodiment, the number of the rotating blades is six. The lengthof the blade portion of the rotating blade becomes longer from about 3"at the first stage to 43" at the final stage. Depending on the output ofthe steam turbine, each of the lengths of the blade portions of thefirst to final rotating blades is set in a range of 80 to 1100 mm; thenumber of stages is 8 or 9; and the length of the blade portion of therotating blade on the downstream side becomes longer than that of theblade portion of the adjacent rotating blade on the upstream side at aratio of 1.2 to 1.8.

The diameter of the rotating blade planted portion is larger than thatof the portion corresponding to the stationary blade. The larger thelength of blade portion of the rotating blade, the larger the width ofthe rotating blade planted portion. The ratio of the width of therotating blade planted portion to the length of the blade portion of therotating blade is in a range of 0.15 to 0.91 and it becomes smallerstepwise in the order from the first stage to the final stage.

The axial root width of the portion, of the rotor shaft, correspondingto the stationary blade becomes smaller stepwise from that between thefirst stage and second stage rotating blades to that between the finalstage rotating blade and the preceding one. The ratio of the axial rootwidth of the portion, of the rotor shaft, corresponding to thestationary blade to the length of the blade portion of the rotatingblade is in a range of 0.25 to 1.25 and it becomes smaller from theupstream side to the downstream side.

The configuration of this embodiment can be applied to a large capacity(1000 MW class) power-generation plant in which the temperature at asteam inlet to each of a high pressure steam turbine and an intermediatepressure steam turbine is set at 610° C. and the temperature at a steaminlet to each of two low pressure steam turbine is set at 385° C.

The high temperature/high pressure steam turbine plant in thisembodiment mainly includes a coal burning boiler, a high pressureturbine, an intermediate pressure turbine, two low pressure turbines, asteam condenser, a condensate pump, a low pressure feed-water heatersystem, a deaerator, a booster pump, a feed-water pump, and a highpressure feed-water heater system. In this turbine plant, ultra-hightemperature/high pressure steam generated by the boiler flows in thehigh pressure turbine to generate a power, being re-heated by theboiler, and flows in the intermediate pressure turbine to generate apower. The steam discharged from the intermediate pressure turbine flowsin the low pressure turbine to generate a power, and is then condensedby the condenser. The condensed water is fed to the low pressurefeed-water heater system and the deaerator by the condensate pump. Thewater deaerated by the deaerator is fed to the high pressure feed-waterheater by the booster pump and the feed-water pump, being heated by theheater, and is then returned into the boiler.

In the boiler, the water is converted into high temperature/highpressure steam by way of an economizer, an evaporator, and asuperheater. Meanwhile, the combustion gas in the boiler used forheating the steam flows out of the economizer, and enters an air heater.In addition, a turbine operated by bleed steam from the intermediatepressure turbine is used for driving the feed-water pump.

In the high temperature/high pressure steam turbine plant having theabove configuration, since the temperature of the feed-water dischargedfrom the high pressure feed-water heater system is very higher than thetemperature of the feed-water in a conventional thermal power plant, thetemperature of the combustion gas discharged from the economizer in theboiler becomes necessarily very higher than that in a conventionalboiler. Accordingly, the heat of the exhaust gas of the boiler isrecovered to lower the gas temperature.

The configuration of this embodiment can be applied to a tandem compoundtype power-generation plant in which a high pressure turbine, anintermediate pressure turbine, and one or two low pressure turbines areconnected in tandem to each other to rotate one generator for powergeneration. In the generator having an output of 1050 MW class in thisembodiment, a generator shaft is made from a material having a highstrength. In particular, there is preferably used a material containing0.15-0.30 wt % of C, 0.1-0.3 wt % of Si, 0.5 wt % or less of Mn,3.25-4.5 wt % of Ni, 2.05-3.0 wt % of Cr, 0.25-0.60 wt % of Mo, and0.05-0.20 wt % of V. This material has a full temper bainite structureand exhibits a tensile strength (at room temperature) of 93 kgf/mm² ormore, preferably, 100 kgf/mm² or more, a 50% FATT of 0° C. or less,preferably, -20° C. or less, and a magnetizing force (at 21.2 KG) of 985AT/cm or less. In this material, further, the total amount of P, S, Sn,Sb and As as impurities is preferably set in a range of 0.025 wt % orless, and a Ni/Cr ratio is preferably set in a range of 2.0 or less.

The high pressure turbine shaft has a structure in which nine stages ofblades are planted on each multi-stage side centered on a first stageblade planted portion. The intermediate pressure turbine shaft isprovided with two sets, each being composed of six stages of blades,disposed substantially symmetrically right and left with respect to anapproximately central portion of the turbine shaft. In addition, whilethe rotor shaft of the low pressure turbine is not shown in any figure,either of the rotor shafts of the high pressure, intermediate pressureand low pressure turbines has a center hole through which the materialquality is checked by ultrasonic inspection, visual inspection andfluorescent penetrant inspection. The material quality of the rotorshaft may be checked from the outer surface side thereof by ultrasonicinspection. In this case, the above center hole may be not formed in therotor shaft.

Table 5 shows chemical compositions (wt %) of materials used for mainportions of the high pressure turbine, intermediate pressure turbine,and low pressure turbine. In this embodiment, the high temperatureportions of the high pressure portion and the intermediate pressureportion are all made from materials having ferrite based crystalstructures exhibiting a thermal expansion coefficient of about 12×10⁻⁶/° C., there is no problem caused by a difference in thermal expansioncoefficient.

The rotor shaft of each of the high pressure turbine and theintermediate pressure turbine was produced by melting 30 ton of a heatresisting cast steel material shown in Table 5 in an electric furnace,followed by deoxidation using carbon in vacuum, and cast in a metalmold. The resultant ingot was forged into an electrode bar, which wasthen melted from top to bottom by electroslag re-melting. Then, theingot was forged into a rotor shape (diameter: 1050 mm, length: 3700mm). The forging was performed at a temperature lower than 1150° C. forpreventing occurrence of forging cracks. The forged steel product wasthen annealed, being heated at 1050° C. and quenched by water spraycooling, and tempered twice at 570° C. and 690° C. The product thusheat-treated was cut into a shape shown in FIGS. 5 and 6. In thisembodiment, the upper side of the ingot formed into the rotor shape,obtained by electroslag re-melting, was taken as the first stage bladeside and the lower side thereof was taken as the final stage blade side.

Each of the blade and nozzle used in the high pressure portion and theintermediate pressure portion was produced by melting a heat resistingsteel material shown in Table 5 in a vacuum arc melting furnace andforging the ingot into a shape of each of the blade and nozzle (width:150 mm, height: 50 mm, length: 1000 mm). The forging was performed at atemperature lower than 1150° C. for preventing occurrence of forgingcracks. The forged steel product was then heated at 1050° C. andoil-quenched, being annealed at 690° C., and cut into a specific shape.

Each of the inner casing, main steam stop valve casing and steamgovernor valve casing in the high pressure portion and the intermediatepressure portion was produced by melting a heat resisting cast steelmaterial shown in Table 5, followed by ladle refining, and casting themolten steel into a sand mold. Since refining and deoxidation weresufficiently performed before casting, any casting defect such as ashrinkage cavity was not found in the cast product. The weldability forthe casing material thus obtained was evaluated in accordance with JISZ3158. In the welding test for evaluation, each of the pre-heatingtemperature, interpass temperature and post-heating starting temperaturewas set at 200° C., and the post-heating treatment was performed under acondition of 400° C.×30 min. As a result of this evaluation test, anywelding crack was not found in the inventive casting material. Thismeans that the inventive casting material is desirable in weldability.

                                      TABLE 5                                     __________________________________________________________________________    (wt. %) psil-14                                                                                                                     Cr                                                                            equi-                   Main parts                                                                              C   Si Mn Ni  Cr Mo W  V  Nb N  Co B   Others                                                                             valent                                                                            Remarks             __________________________________________________________________________    High                                                                              Rotor 0.11                                                                              0.03                                                                             0.52                                                                             0.49                                                                              10.98                                                                            0.19                                                                             2.60                                                                             0.21                                                                             0.07                                                                             0.019                                                                            2.70                                                                             0.015                                                                             --   5.11                                                                              Forged              pressure                                              (≦9.5)                                                                     steel               portion                                                                           Blade (first                                                                        0.10                                                                              0.04                                                                             0.47                                                                             0.51                                                                              11.01                                                                            0.15                                                                             2.62                                                                             0.19                                                                             0.08                                                                             0.020                                                                            2.81                                                                             0.016                                                                             --   5.07                                                                              Forged              and stage)                                            (≦10)                                                                      steel               inter-                                                                            Nozzle                                                                              0.09                                                                              0.04                                                                             0.55                                                                             0.59                                                                              10.50                                                                            0.14                                                                             2.54                                                                             0.18                                                                             0.06                                                                             0.015                                                                            2.67                                                                             0.013                                                                             --   4.54                                                                              Forged              mediate                                                                           (first                                            (≦10)                                                                      steel               pressure                                                                          stage)                                                                    portion                                                                           Inner casing                                                                        0.12                                                                              0.19                                                                             0.50                                                                             0.68                                                                              8.95                                                                             0.60                                                                             1.68                                                                             0.18                                                                             0.06                                                                             0.040                                                                            -- 0.002                                                                             --   7.57                                                                              Cast                                                                          steel                   Outer casing                                                                        0.12                                                                              0.21                                                                             0.32                                                                             0.08                                                                              1.51                                                                             1.22                                                                             -- 0.22                                                                             -- -- -- 0.0007                                                                            Ti0.05                                                                             --  Cast                                                                 A10.010  steel                   Inner casing                                                                        0.11                                                                              0.10                                                                             0.50                                                                             0.60                                                                              10.82                                                                            0.23                                                                             2.80                                                                             0.23                                                                             0.08                                                                             0.021                                                                            3.00                                                                             0.020                                                                             --   4.72                                                                              Forged                  fastening                                             steel                   bolt                                                                      Low Rotor 0.25                                                                              0.03                                                                             0.04                                                                             3.68                                                                              1.75                                                                             0.36                                                                             -- 0.13                                                                             -- -- -- --  --   --  Forged              pressure                                                  steel               portion                                                                           Blade 0.11                                                                              0.20                                                                             0.53                                                                             0.39                                                                              12.07                                                                            0.07                                                                             -- -- -- -- -- --  --   --  Forged                                                                        steel                   Nozzle                                                                              0.12                                                                              0.18                                                                             0.50                                                                             0.43                                                                              12.13                                                                            0.10                                                                             -- -- -- -- -- --  --   --  Forged                                                                        steel                   Inner casing                                                                        0.25                                                                              0.51                                                                             -- --  -- -- -- -- -- -- -- --  --   --  Cast                                                                          steel                   Outer casing                                                                        0.24                                                                              0.50                                                                             -- --  -- -- -- -- -- -- -- --  --   --  Cast                                                                          steel               Casing for main steam                                                                   0.10                                                                              0.19                                                                             0.48                                                                             0.65                                                                              8.96                                                                             0.60                                                                             1.62                                                                             0.20                                                                             0.05                                                                             0.042                                                                            -- 0.002                                                                             --   9.56                                                                              Cast                stop valve                                                steel               Casing for steam                                                                        0.12                                                                              0.21                                                                             0.52                                                                             0.63                                                                              9.00                                                                             0.63                                                                             1.70                                                                             0.17                                                                             0.06                                                                             0.039                                                                            -- 0.001                                                                             --   7.97                                                                              Cast                governor valve                                            steel               __________________________________________________________________________

Table 6 shows results of examining mechanical properties of the mainmembers cut off from the above ferrite based steel made high temperaturesteam turbine, and heat-treatment conditions.

As a result of examining mechanical properties of a central portion ofthe rotor shaft, it was confirmed that the mechanical properties of thecentral portion sufficiently satisfy characteristics (10⁵ h creeprupture strength (at 625° C.)≧10 kgf/mm² ; impact absorption energy (at20° C.)≧1.5 kgf-m) required for rotors of the high pressure andintermediate pressure turbines. This verifies that a steam turbine rotorusable in steam at a temperature of 620° C. or more can be produced.

As a result of examining mechanical properties of the blade, it wasconfirmed that the mechanical properties of the blade sufficientlysatisfy characteristics (10⁵ h creep rupture strength (at 625° C.)≧15kgf/mm²) required for first stage blades of the high pressure andintermediate pressure turbines. This verifies that a steam turbine bladeusable in steam at a temperature of 620° C. or more can be produced.

As a result of examining mechanical properties of the casing, it wasconfirmed that the mechanical properties of the casing sufficientlysatisfy characteristics (10⁵ h creep rupture strength (at 625° C.)≧10kgf/mm² ; impact absorption energy (at 20° C.)≧1 kgf-m) required forcasings of the high pressure and intermediate pressure turbines andfurther the casing material is weldable. This verifies that a steamturbine casing usable in steam at a temperature of 620° C. or more canbe produced.

                                      TABLE 6                                     __________________________________________________________________________    pail-14                                                                                                Reduc-      10.sup.3 h creep rap-                                    0.2%     tion        ture strength                                      Tensile                                                                             proof                                                                              Elonga-                                                                           of  Impact  (kgf/mm.sup.2)                                     strength                                                                            stress                                                                             tion                                                                              area                                                                              value                                                                             FATT                                                                              625°                                                                      575°                                                                      450°                        Main parts                                                                              (kgf/mm.sup.2)                                                                      (kgf/mm.sup.2)                                                                     (%) (%) (kgf-m)                                                                           (%) C. C. C. Heat treatment                  __________________________________________________________________________                                                  condition                       High                                                                              Rotor 90.5  76.6 20.6                                                                              66.8                                                                              3.8  40 17.0                                                                             -- -- 1050° C. × 15                                                    h→water spray                                                          cooling,                        pressure                                      570° C. × 20                                                     h→furnace cooling,       portion                                       690° C. × 20                                                     h→furnace cooling        and Blade 93.4  81.5 20.9                                                                              69.8                                                                              4.1 --  18.1                                                                             -- -- 1075° C. × 1.5                                                   h→oil cooling,           inter-                                        740° C. × 5                                                      h→air cooling            mediate                                                                           Nozzle                                                                              93.0  80.9 21.4                                                                              70.3                                                                              4.8 --  17.8                                                                             -- -- 1050° C. × 1.5                                                   h→oil cooling,           pressure                                      690° C. × 5                                                      h→air cooling            portion                                                                           Inner 79.7  60.9 19.8                                                                              65.3                                                                              5.3 --  11.2                                                                             -- -- 1050° C. × 8                                                     h→air blast                                                            cooling,                            casing                                    600° C. × 20                                                     h→furnace cooling,                                                     730° C. × 10                                                     h→furnace cooling            Outer 69.0  53.8 21.4                                                                              65.4                                                                              1.5 --  -- 12.                                                                              -- 1050° C. × 8                                                     h→air blast                                                            cooling,                            casing                              5     725° C. × 10                                                     h→furnace cooling            Inner cas-                                                                          107.1 91.0 19.5                                                                              88.7                                                                              2.0 --  18.0                                                                             -- -- 1075° C. × 2                                                     h→oil cooling,               ing fasten-                               740° C. × 5                                                      h→air cooling                ing bolt                                                                  Low Rotor 91.8  80.0 22.0                                                                              70.1                                                                              19.1                                                                              -50 -- -- 36 950° C. × 30                                                     h→water spray                                                          cooling,                        pressure                                      605° C. × 45                                                     h→furnace cooling        portion                                                                           Blade 80.0  66.0 22.1                                                                              67.5                                                                              3.5 --  -- -- 27 950° C. × 1.5                                                    h→oil cooling,                                                         605° C. × 5                                                      h→air cooling                Nozzle                                                                              79.8  65.7 22.4                                                                              69.6                                                                              3.8 --  -- -- 26 950° C. × 1.5                                                    h→oil cooling,                                                         605° C. × 1.5                                                    h→air cooling                Inner 41.5  22.2 22.2                                                                              81.0                                                                              --  --  -- -- -- --                                  casing                                                                        Outer 41.1  20.3 24.5                                                                              80.5                                                                              --  --  -- -- -- --                                  casing                                                                    Casing for main steam                                                                   77.0  61.0 18.6                                                                              65.0                                                                              2.5 --  11.2                                                                             -- -- 1050° C. × 8                                                     h→air blast                                                            cooling,                        stop valve                                    600° C. × 20                                                     h→furnace cooling,                                                     730° C. × 10                                                     h→furnace cooling        Casing for steam                                                                        77.5  61.6 18.2                                                                              64.6                                                                              2.4 --  11.0                                                                             -- -- 1050° C. × 8                                                     h→air blast                                                            cooling,                        governor valve                                600° C. × 20                                                     h→furnace cooling,                                                     730° C. × 10                                                     h→furnace                __________________________________________________________________________                                                  cooling                     

In this embodiment, a Cr--Mo low alloy steel was built up by welding ona journal portion of the rotor shaft for improving a bearingcharacteristic. The buildup welding is performed as follows:

As a test welding rod, there was used a coated electrode (diameter:4.0Φ. The chemical composition (wt %) of a weld metal obtained bywelding using the coated electrode is shown in Table 7. The compositionof the weld metal is nearly equal to that of the welding material.

The welding condition is set such that the welding current is 170 A; thewelding voltage is 24 V; and the welding speed is 26 cm/min.

                  TABLE 7                                                         ______________________________________                                        No.  C      Si     Mn   P    S    Ni   Cr   Mo   Fe                           ______________________________________                                        A    0.06   0.45   0.65 0.010                                                                              0.011                                                                              --   7.80 0.50 Balance                      B    0.03   0.65   0.70 0.009                                                                              0.008                                                                              --   5.13 0.53 "                            C    0.03   0.79   0.56 0.009                                                                              0.012                                                                              0.01 2.34 1.04 "                            D    0.03   0.70   0.90 0.007                                                                              0.016                                                                              0.03 1.30 0.57 "                            ______________________________________                                    

On the surface of the above-described test base material were built upeight layers using respective welding rods as shown in Table 8. Thethickness of each layer was 3-4 mm, and the total thickness of the eightlayers was about 28 mm. The surface portion of the buildup layers wasground about 5 mm.

The welding procedure conditions are set such that each of thepre-heating temperature, interpass temperature, and stress reliefannealing (SR) starting temperature is in a range of 250 to 350° C., andthe SR treatment is performed under a condition of 250 to 35 of 630°C.×36 h.

                  TABLE 8                                                         ______________________________________                                        First Second  Third   Fourth                                                                              Fifth Sixth                                                                              Seventh                                                                             Eighth                           layer layer   layer   layer layer layer                                                                              layer layer                            ______________________________________                                        A     B       C       D     E     F    G     H                                ______________________________________                                    

To check characteristics of the welded portion, the above buildupwelding was repeated except for use of a plate as a base material. Theweld portion of the plate was subjected to 160° side bending test, as aresult of which any crack was not found in the welding portion.

The journal portion of the rotor shaft of the present invention was alsosubjected to bearing sliding test. As a result, it was confirmed thatthe journal portion did not exert any adverse effect on the bearing, andwas also desirable in oxidation resistance.

The configuration of this embodiment can be applied to a tandem typepower-generation plant in which a high pressure turbine, an intermediatepressure turbine, and one or two low pressure turbines are connected intandem to be rotated at 3600 rpm, and further, the combination of thehigh pressure turbine, intermediate pressure turbine and low pressureturbine can be also applied to the turbine configuration B shown inTable 4.

[Embodiment 3]

Table 9 shows a main specification of a steam turbine in which the steamtemperature is set at 600° C. and the plant output is set at 600 MW. Inthis embodiment, the steam turbine is of a tandem compound/double-flowtype, and the length of a final stage blade in a low pressure turbine is43 inches. A turbine configuration C has a turbine combination of[(HP/IP) integral type+LP] and a turbine configuration D has a turbinecombination of [(HP/IP) integral type+2×LP], each of which is operatedat the number of revolution of 3000 rpm. Main components in the highpressure portion are made from materials shown in Table 9. In the hightemperature portion (HP), the steam temperature is 600° C. and the steampressure is 250 kgf/cm². The steam supplied from the HP portion isheated to 600° C. by a re-heater and is supplied to the intermediatepressure portion (IP). The intermediate pressure portion is operated atthe steam temperature 600° C. and at a steam pressure of 45 to 65kgf/cm². The steam at a steam temperature of 400° C. is supplied in thelow pressure portion (LP), and the steam at a steam temperature of 100°C. or less and in a vacuum of 722 mm Hg is supplied to a steamcondenser.

                                      TABLE 9                                     __________________________________________________________________________    Type of turbine                                                                              TCDF-43                                                        Number of revolution                                                                         3000/3000 RPM                                                  Steam condition                                                                              25 Mpa-600° C./600° C.                           Configuration of turbine                                                                 C                                                                                  ##STR3##                                                                 D                                                                                  ##STR4##                                                      Structure of first stage blade                                                               2 tenon saddle type dovetail blade                             Final stage blade                                                                            Titanium alloy made 43 inch long                                              blade or high-strength 12Cr forged                                            steel                                                          Main steam stop valve body,                                                                  High-strength 12Cr forged steel                                Steam governor valve body                                                     High/intermediate pressure rotor                                                             High-strength 12Cr forged steel                                Low pressure rotor                                                                           3.5Ni--Cr--Mo--V forged steel                                  Rotating blade at high                                                                       First stage:                                                   temperature portion                                                                          high-strength 12Cr forged steel                                High/intermediate pressure casing                                             Interior       High-strength 9Cr cast steel                                   Exterior       High-strength Cr--Mo--V--B cast steel                          Gross thermal efficiency (Rated                                                              47.1%                                                          output, end of generator)                                                     __________________________________________________________________________     (TCDF-43: tandem compound type doubleflow exhaust, 43 inch long blade HP:     high pressure portion, IP: intermediate pressure portion, LP: low pressur     portion, R/H: reheater (boiler))                                         

FIG. 11 is a sectional configuration view showing the high pressure sideturbine-intermediate pressure side turbine integral type steam turbine,and FIG. 12 is a sectional view of a rotor shaft used in the steamturbine shown in FIG. 11. The high pressure side steam turbine has ahigh pressure/intermediate pressure axle (high pressure rotor shaft) 23disposed inside an inner casing 18 and an outer casing 19 positionedoutside the inner casing 18. High pressure side rotating blades 16 areplanted in the high pressure rotor shaft 23. The above steam at a hightemperature and a high pressure is produced by the above boiler, passingthrough a main steam pipe, a flange constituting a main steam inletportion and an elbow 25, a main steam inlet 28, and is introduced to afirst stage rotating blade from a nozzle box 38. Eight stages ofrotating blades are provided on the high pressure side (left side in thefigure), and six stages of rotating blades are provided on theintermediate pressure side (on about half of the right side in thefigure). Stationary blades are provided in such a manner as to bematched with these rotating blades. The rotating blade is of a saddle or"geta" (Japanese wooden sandal) shaped dovetail type having doubletenons. The length of the first stage blade on the high pressure side isabout 40 mm, and the length of the first stage blade on the intermediatepressure side is 100 mm. The distance between centers of bearings 43 isabout 6.7 m. The diameter of the minimum one of portions correspondingto the stationary blades is about 740 mm, and the ratio of thebetween-bearing distance to this diameter is about 9.0.

As for the axial root widths of rotating blade planted portions of thehigh pressure side rotor shaft, the axial root width at the first stageis widest; the axial root widths at the second to seventh stages aresubstantially equal to each other, each of which is smaller 0.40-0.56times than that at the first stage; and the axial root width at thefinal stage is intermediate between that at the first stage and that ateach of the second to seventh stages, and which is smaller 0.46-0.62times than that at the first stage.

The blade and nozzle on the high pressure side are made from a 12% Crbased steel shown in Table 5 (which will be described later). The lengthof a blade portion of the rotating blade in this embodiment is in arange of 35 to 50 mm at the first stage, and becomes longer in thedirection from the second stage to the final stage. In particular,depending on the output of the steam turbine, each of the lengths of theblade portions of the second to final rotating blades is set in a rangeof 50 to 150 mm; the number of stages is set in a range of 7 to 12; andthe length of the blade portion of the rotating blade on the downstreamside becomes longer than that of the blade portion of the adjacentrotating blade on the upstream side at a ratio of 1.05 to 1.35, and theratio becomes gradually larger toward the downstream side.

The intermediate pressure side steam turbine is operated to rotate agenerator together with the high pressure side steam turbine by thesteam which is discharged from the high pressure side steam turbine andheated again at 600° C. by a reheater. The intermediate pressure sidesteam turbine is rotated at 3000 rpm. The intermediate pressure sideturbine has intermediate pressure inner and outer casings 21 and 22 likethe high pressure side turbine. Stationary blades are providedcorrespondingly to intermediate pressure rotating blades 17. Six stagesof the rotating blades 17 are provided. The length of the first stageblade is about 130 mm, and the length of the final stage blade is about260 mm. The dovetail is formed into an inverse-chestnut shape. Thediameter of a portion, of the rotor shaft, corresponding to thestationary blade is about 740 mm.

As for the axial root widths of rotating blade planted portions of therotor shaft of the intermediate pressure steam turbine, the axial rootwidth at the first stage is widest; the axial root width at the secondstage is smaller than that at the first stage; the axial root widths atthe third to fifth stages are equal to each other, each of which issmaller than that at the second stage; and the axial root width at thefinal stage is intermediate between that at the second stage and that ateach of the third to fifth stages, and which is smaller 0.48-0.64 timesthan that at the first stage. The axial root width at the first stage islarger about 1.1-1.5 times than that at the second stage.

The blade and nozzle on the intermediate pressure side are made from a12% Cr based steel shown in Table 5 (which will be described later). Thelength of a blade portion of the rotating blade in this embodimentbecomes longer in the direction from the first stage to the final stage.In particular, depending on the output of the steam turbine, each of thelengths of the blade portions of the first to final rotating blades isset in a range of 90 to 350 mm; the number of stages is set in a rangeof 6 to 9; and the length of the blade portion of the rotating blade onthe downstream side becomes longer than that of the blade portion of theadjacent rotating blade on the upstream side at a ratio of 1.10 to 1.25.

The diameter of the rotating blade planted portion is larger than thatof the portion corresponding to the stationary blade. The width of therotating blade planted portion is dependent on the length of the bladeportion and the position of the rotating blade. The ratio of the widthof the rotating blade planted portion to the length of the blade portionof the rotating blade is widest at the first stage (1.35 to 1.8 times),becomes slightly smaller at the second stage (0.88 to 1.18 times), andbecomes gradually smaller toward the final stage at third to sixthstages (0.40 to 0.65 times).

FIG. 13 is a sectional view of the low pressure turbine, and FIG. 14 isa sectional view of a rotor shaft of the low pressure turbine shown inFIG. 13. One low pressure turbine is connected in tandem with the highpressure/intermediate pressure sides. Two sets, each being composed ofsix stages of rotating blades 41, are disposed substantiallysymmetrically right and left. Stationary blades 42 are disposed in sucha manner as to be matched with the rotating blades. The final stagerotating blade has a length of 43 inches, and is made from a 12% Crbased steel or a Ti based alloy shown in Table 1. The Ti based alloycontains 16 wt % of Al and 4 wt % of V and is subjected to age-hardeningtreatment. A rotor shaft 43 is made from a super clean forged steelhaving a full temper bainite structure. To be more specific, the forgedsteel contains 3.75 wt % of Ni, 1.75 wt % of Cr, 0.4 wt % of Mo, 0.15 wt% of V, 0.25 wt % of C, 0.05 wt % of Si and 0.10 wt % of Mn, the balancebeing Fe. The rotating blades other than the final state one and thepreceding stage one and the stationary blades are made from a 12% Crbased steel containing 0.1 wt % of Mo. The inner and outer casings aremade from a cast steel containing 0.25 wt % of C. In this embodiment,the distance between centers of bearings 43 is 7000 mm; the diameter ofa portion, of the rotor shaft, corresponding to the stationary blade isabout 800 mm. The diameter of the rotating blade planted portion of therotor shaft is not changed at the first to final stages. The ratio ofthe between-bearing distance to the diameter of the portion, of therotor shaft, corresponding to the stationary blade is about 8.8.

The axial root width of the rotating blade planted portion of the rotorshaft of the low pressure turbine is smallest at the first stage, andbecomes gradually larger to the downstream side in four stages. Theaxial root width at the second stage is equal to that at the thirdstage, and the axial root width at the fourth stage is equal to that atthe fifth stage. The axial root width at the final stage is larger6.2-7.0 times than that at the first stage. The axial root width at eachof the second and third stages is larger 1.15-1.40 times than that atthe first stage; the axial root width at each of the fourth and fifthstages is larger 2.2-2.6 times than that at each of the second and thirdstages; and the axial root width at the final stage is larger 2.8-3.2times than that at each of the fourth and fifth stages. In the figure,the width of a rotating blade planted portion is indicated by a distancebetween two points at which the downward extended lines of the rotatingblade planted portion cross the diameter of the rotor shaft.

In this embodiment, the length of the blade portion of the rotatingblade becomes longer from about 4" at the first stage to 43" at thefinal stage. Depending on the output of the steam turbine, each of thelengths of the blade portions of the first to final rotating blades isin a range of 100 to 1270 mm; the number of stages is 8 at maximum; andthe length of the blade portion of the rotating blade on the downstreamside becomes longer than that of the blade portion of the adjacentrotating blade on the upstream side at a ratio of 1.2 to 1.9.

As compared with the shape of the portion corresponding to thestationary blade, the shape of the rotating blade planted portion isextended downward. The larger the length of the blade portion of therotating blade, the larger the width of the rotating blade plantedportion. The ratio of the width of the rotating blade planted portion tothe length of the blade portion of the rotating blade, which is in arange of 0.30 to 1.5, becomes gradually smaller from the first stage tothe stage directly before the final stage. On the downstream side, theratio at one stage becomes smaller 0.15-0.40 times than that at thepreceding stage thereof. The ratio at the final stage is in a range of0.50 to 0.65.

The final stage rotating blade in this embodiment is the same as thatdescribed in Embodiment 2. FIG. 15 is a perspective view, with anessential portion cutaway, showing a state in which an erosion shield(stellite alloy) 54 is joined by electron beam welding or TIG welding asindicated by reference numeral 56. As shown in the figure, the shield 54is welded at two points on the front and back sides.

The configuration of this embodiment can be applied to a large capacity(1000 MW class) power-generation plant in which the temperature at asteam inlet to a high pressure/intermediate pressure steam turbine is610° C. or more and temperatures of a steam inlet and a steam outlet toand from a low pressure steam turbine are about 400° C. and about 60° C.respectively.

The high temperature/high pressure steam turbine power-generation plantin this embodiment mainly includes a boiler, a highpressure/intermediate pressure turbine, a low pressure turbine, a steamcondenser, a condensate pump, a low pressure feed-water heater system, adeaerator, a booster pump, a feed-water pump, and a high pressurefeed-water heater system. Ultra-high temperature/high pressure steamgenerated by the boiler flows in the high pressure side turbine togenerate a power, being re-heated by the boiler, and flows in theintermediate pressure side turbine to generate a power. The steamdischarged from the high pressure/intermediate pressure turbine flows inthe low pressure turbine to generate a power, and is then condensed bythe condenser. The condensed water is fed to the low pressure feed-waterheater system and the deaerator by the condensate pump. The waterdeaerated by the deaerator is fed to the high pressure feed-water heaterby the booster pump and the feed-water pump, being heated by the heater,and is then returned into the boiler.

In the boiler, the water is converted into high temperature/highpressure steam by way of an economizer, an evaporator, and asuperheater. Meanwhile, the combustion gas in the boiler used forheating the steam flows out of the economizer, and enters an air heater.In addition, a turbine operated by bleed steam from the intermediatepressure turbine is used for driving the feed-water pump.

In the high temperature/high pressure steam turbine plant having theabove configuration, since the temperature at the feed-water dischargedfrom the high pressure feed-water heater system is very higher than thetemperature of the feed-water in a conventional thermal power plant, thetemperature of the combustion gas discharged from the economizer in theboiler becomes necessarily very higher than that in a conventionalboiler. Accordingly, the heat of the exhaust gas of the boiler isrecovered to lower the gas temperature.

Although in this embodiment, the present invention is applied to thetandem compound/double flow type power-generation plant in which onehigh pressure/intermediate pressure turbine and one low pressure turbineare connected in tandem with one generator, the present invention can bealso applied to the turbine configuration D having a large output of1050 MW class, shown in Table 9, which is characterized in that two lowpressure turbines are connected in tandem with each other. In thegenerator having an output of 1050 MW class, a generator shaft is madefrom a material having a high strength. In particular, there ispreferably used a material containing 0.15-0.30 wt % of C, 0.1-0.3 wt %of Si, 0.5 wt % or less of Mn, 3.25-4.5 wt % of Ni, 2.05-3.0 wt % of Cr,0.25-0.60 wt % of Mo, and 0.05-0.20 wt % of V. This material has a fulltemper bainite structure and exhibits a tensile 0.05-0.20 wt % of V.This strength (at room temperature) of 93 kgf/mm² or more, preferably,100 kgf/mm² or more, a 50% FATT of 0° C. or less, preferably, -20° C. orless, and a magnetizing force (at 21.2 KG) of 985 AT/cm or less. In thismaterial, further, the total amount of P, S, Sn, Sb and As as impuritiesis preferably set in a range of 0.025 wt % or less, and a Ni/Cr ratio ispreferably set in a range of 2.0 or less.

Table 5 (described above) shows chemical compositions (wt %) ofmaterials used for main portions of the high pressure/intermediatepressure turbine and the low pressure turbine. In this embodiment, themain portions are all made from materials, shown in Table 5, havingferrite based crystal structures exhibiting a thermal expansioncoefficient of about 12×10⁻⁶ /° C. except that the high temperatureportion at which the high pressure side is integrated with theintermediate pressure side is made from a martensite steel representedby Sample No. 9 in Embodiment 4 to be described later, there is noproblem caused by a difference in thermal expansion coefficient.

The rotor shaft of the high pressure/intermediate pressure portion wasproduced by melting 30 ton of a heat resisting cast steel materialrepresented by Sample No. 1 in Table 10 in an electric furnace, followedby deoxidation using carbon in vacuum, and cast in a metal mold. Theresultant ingot was forged into an electrode bar, which was then meltedfrom top to bottom by electroslag re-melting. Then, the ingot was forgedinto a rotor shape (diameter: 1450 mm, length: 5000 mm). The forging wasperformed at a temperature lower than 1150° C. for preventing occurrenceof forging cracks. The forged steel product was then annealed, beingheated at 1050° C. and quenched by water spray cooling, and temperedtwice at 570° C. and 690° C. The product thus heat-treated was cut intoa shape shown in FIG. 12.

Materials of other portions and producing conditions thereof are thesame as those in Embodiment 2. Further, a bearing journal portion 45 wassubjected to buildup welding in the same manner as that in Embodiment 2.

[Embodiment 4]

In this embodiment, each of alloys having compositions shown in Table 10was melted in vacuum and cast into an ingot of 10 kg. The ingot was thenforged into a shape of 30 mm×30 mm. For produced of a large-sized steamturbine shaft and a blade thereof, the forged product was subjected tothe following heat-treatments under conditions determined by simulationof an actual operating condition of the central portion of the rotorshaft. For the rotor shaft, the forged product was kept at 1050° C. for5 h and quenched by cooling at a cooling rate of 100° C./h (at thecenter portion). The quenched product was then subjected to primarytemper under a condition of 570° C.×20 h and secondary temper under acondition of 690° C.×20 h. For the blade, the forged product was kept at1100° C. for 1 h, followed by quenching, and was subjected to temperunder a condition of 750° C.×1 h. Each of the resultant products for therotor shaft and the blade was subjected to creep rupture test under acondition of 625° C.-30 kgf/mm². The results are shown in Table 7.

The inventive alloys, represented by Sample Nos. 1 to 6 in Table 10 areproved to be long in creep rupture life and thereby desired to be usedin a steam condition having a steam temperature of 620° C. or more.Although an increase in Co content prolongs the creep rupture time, aproduct made from the alloy containing Co in an excessively large amounttends to cause embrittlement when heated at a temperature of 600 to 660°C. To improve both the strength and toughness of a product made from thealloy containing Co, the alloy preferably contains Co in an amount of 2to 5 wt % for the product used at a temperature of 620 to 630° C., andit preferably contains Co in an amount of 5.5 to 8 wt % for the productused at a temperature of 630 to 660° C. The element B exhibits astrength increasing effect in the case where the B content is in a rangeof 0.03 wt % or less. The alloy, which is adopted as a material of aproduct used in a temperature range of 620 to 630° C., preferablycontains B in an amount of 0.001 to 0.01 wt % and Co in an amount of 2to 4 wt % for increasing the strength of the product; and the alloy,which is adopted as a material of a product used on the highertemperature side, specifically, in a temperature range of 630 to 660°C., preferably contains B in an amount of 0.01 to 0.03 wt % and Co in anamount of 5 to 7.5 wt % for increasing the strength of the product.

As for the content of N, it became apparent that the alloy containing Nin a smaller amount exhibits a strength higher than that of the alloycontaining N in a larger amount, when the alloy is used at a temperatureof 600° C. or more as in this embodiment. The N content is preferably ina range of 0.01 to 0.04 wt %. The element N is little contained in thealloy upon vacuum-melting, and therefore, it is added in the form of amother alloy.

As shown in Table 10, the rotor material is equivalent to Sample No. 2prepared in this embodiment, which exhibits a high strength. Sample No.8 in which the Mn content is as low as 0.09% exhibits a higher strengthas compared with a different sample, shown in Table 10, containing thesame Co content as that of Sample No. 8, and therefore, to increase thestrength of the alloy, the alloy preferably contains Mn in an amount of0.03 to 0.20 wt %.

                                      TABLE 10                                    __________________________________________________________________________                                             Creep rapture                                                                 strength (h)                                                                  625° C.-30 kgf/mm.sup.2          Chemical composition (wt %)           Rotor                                No.                                                                              C  Si Mn Ni Cr Mo W  V  Nb Co N  B  Fe                                                                              shaft                                                                              Blade                           __________________________________________________________________________    1  0.11                                                                             0.01                                                                             0.50                                                                             0.54                                                                             10.72                                                                            0.15                                                                             2.61                                                                             0.20                                                                             0.09                                                                             2.15                                                                             0.025                                                                            0.014                                                                            Bal                                                                             140  278                             2  0.11                                                                             0.01                                                                             0.50                                                                             0.50                                                                             10.98                                                                            0.15                                                                             2.59                                                                             0.21                                                                             0.09                                                                             2.87                                                                             0.025                                                                            0.014                                                                            " 161  315                             3  0.11                                                                             0.01                                                                             0.51                                                                             0.53                                                                             11.00                                                                            0.16                                                                             2.55                                                                             0.22                                                                             0.08                                                                             5.79                                                                             0.027                                                                            0.015                                                                            " 241  508                             4  0.11                                                                             0.01                                                                             0.48                                                                             0.49                                                                             11.03                                                                            0.18                                                                             2.60                                                                             0.19                                                                             0.08                                                                             9.43                                                                             0.030                                                                            0.016                                                                            " 240  488                             5  0.12                                                                             0.01                                                                             1.30                                                                             0.11                                                                             11.24                                                                            0.20                                                                             2.65                                                                             0.18                                                                             0.11                                                                             2.98                                                                             0.051                                                                            0.003                                                                            " 192  392                             6  0.13                                                                             0.01                                                                             0.15                                                                             0.89                                                                             11.35                                                                            0.09                                                                             2.91                                                                             0.27                                                                             0.10                                                                             4.50                                                                             0.045                                                                            0.927                                                                            " 219  456                             __________________________________________________________________________

Table 11 shows chemical compositions (wt %) of materials for rotorshafts suitable to be used at a temperature condition of a 600° C.class. The heat-treatment was performed by keeping the sample at 1100°C. for 2 h and cooling it at a cooling rate of 100° C./h; and heatingthe sample at 565° C. for 15 h and cooling it at a cooling rate of 20°C./h and heating again the sample at 665° C. for 45 h and cooling it ata cooling rate of 20° C./h. In this heat-treatment, each rotor shaftmaterial was turned around its rotating shaft.

Table 12 shows mechanical properties of the rotor shaft materials. Theimpact value is represented by the Charpy V-notch value, and the FATT isrepresented by the 50% fracture appearance transition temperature.

                                      TABLE 11                                    __________________________________________________________________________                                        Cr                                        No.                                                                              C  Si Mn Ni Cr Mo V  Nb N  W  Al equivalent                                __________________________________________________________________________    7  0.17                                                                             0.21                                                                             0.57                                                                             0.60                                                                             11.15                                                                            1.29                                                                             0.22                                                                             0.07                                                                             0.049                                                                            0.24                                                                             0.007                                                                            8.89                                      8  0.18                                                                             0.24                                                                             0.60                                                                             0.59                                                                             11.20                                                                            1.24                                                                             0.19                                                                             0.06                                                                             0.048                                                                            0.41                                                                             0.019                                                                            8.41                                      9  0.17                                                                             0.22                                                                             0.57                                                                             0.60                                                                             11.10                                                                            1.24                                                                             0.21                                                                             0.06                                                                             0.045                                                                            0.49                                                                             0.015                                                                            9.04                                      __________________________________________________________________________

                  TABLE 12                                                        ______________________________________                                                              Reduc-            600° C., 10.sup.5 h                                  tion              creep                                      Tensile  Elonga- of    Impact      rapture                                    strength tion    area  value FATT  strength                              No.  (kgf/mm.sup.2)                                                                         (%)     (%)   (kgf-m)                                                                             (° C.)                                                                       (kgf/mm.sup.2)                        ______________________________________                                        7    90.5     20.1    60.0  2.05  49    11.6                                  8    90.4     20.0    58.1  1.97  52    10.8                                  9    91.0     19.5    58.3  2.00  56    11.7                                  ______________________________________                                    

As shown in Table 12, each of the inventive materials exhibits a 10⁵ hcreep rupture strength (at 600° C.) of 11 kgf/mm², and also exhibits astrength higher than a value (10 kgf/mm²) required as a high efficientturbine material and a toughness higher than a value (1 kgf-m) requiredas the high efficient turbine material.

Sample No. 8, which contains Al in an amount more than 0.015 wt %, isslightly reduced in strength, concretely, it exhibits a 10⁵ h creeprupture strength less than 11 kgf/mm². It was confirmed that when thecontent of W in the alloy is increased up to about 1.0 wt %, thereoccurs precipitation of δ ferrite, leading to reduction in both thestrength and toughness of the alloy. Accordingly, the W contentincreased up to about 1.0 wt % fails to achieve the object of thepresent invention.

The W content in an amount of 0.1 to 0.65 wt % is effective to increasethe strength of the alloy.

As for the effect of the W content on the FATT, the FATT is low, thatis, the toughness is high with the W content kept in a range of 0.1 to0.65 wt %; however, the toughness becomes lower with the W contentoffset from the above range. The W content in a range of 0.2 to 0.5 wt %is particularly effective to low the FATT.

The martensite steel in this embodiment, which is significantly high increep rupture strength at a high temperature near 600° C., sufficientlysatisfies the strength required for a rotor shaft for ultra-high/highpressure steam turbine, and therefore, it is suitable for such a rotorshaft; and also it is suitable for a blade for a high efficient turbineoperated at a temperature near 600° C.

[Embodiment 5]

Table 13 shows chemical compositions (wt %) of inner casings for a highpressure turbine, an intermediate pressure turbine, and a highpressure/intermediate pressure turbine of the present invention. Asample having a size determined in consideration of a thick wall portionof a large size casing was produced by melting 200 kg of a materialshown in Table 13 in a high frequency induction melting furnace, andcast in a sand mold having a maximum thickness of 200 mm, a width of 380mm, and a height of 440 mm, to prepare an ingot. The sample thusobtained was subjected to annealing (1050° C.×8 h→furnace cooling), andthen subjected to heat-treatments suitable for a thick wall portion of alarge-sized steam turbine casing, that is, normalizing (1050° C.×8 h→aircooling) and temper (twice, 710° C.×7 h→air cooling+710° C.×7 h→aircooling).

The weldability of the sample was evaluated in accordance with JISZ3158. Each of the pre-heating temperature, interpass temperature, andpost-heating temperature stating temperature was set at 150° C., and thepost-heating treatment was performed in a condition of 400° C.×30 min.

                                      TABLE 13                                    __________________________________________________________________________    No.                                   Cr equi-                                Sample                                                                            C  Si Mn Ni Cr Mo W  V  Nb N  W   velnt                                                                             Ni/W                                __________________________________________________________________________    1   0.12                                                                             0.22                                                                             0.51                                                                             0.80                                                                             9.05                                                                             0.59                                                                             1.59                                                                             0.21                                                                             0.06                                                                             0.05                                                                             0.0031                                                                            7.13                                                                              0.52                                2   0.13                                                                             0.20                                                                             0.50                                                                             0.61                                                                             8.97                                                                             0.11                                                                             1.60                                                                             0.19                                                                             0.07                                                                             0.05                                                                             0.0019                                                                            5.31                                                                              0.38                                3   0.12                                                                             0.20                                                                             0.48                                                                             0.61                                                                             9.00                                                                             0.62                                                                             1.66                                                                             0.19                                                                             0.07                                                                             0.03                                                                             0.0010                                                                            8.21                                                                              0.37                                __________________________________________________________________________

Table 14 shows results of examining the tensile characteristic at roomtemperature, Charpy V-notch impact absorption energy at 20° C., 10⁵ hcreep rupture strength, and welding crack for each sample shown in Table13.

The creep rupture strength and impact absorption energy of the inventivematerial containing B, Mo and W in suitable amounts sufficiently satisfycharacteristics (10⁵ h creep rupture strength (at 625° C.)≧8 kgf/mm²,impact absorption energy (at 20° C.)≧1 kgf-m) required for a hightemperature/high pressure turbine casing. In particular, the inventivematerial exhibits a high 10⁵ h creep rupture strength (at 625° C.) of 9kgf/mm² or more. In the inventive material there occurs no weldingcrack. This means that the inventive material is good in weldability. Asa result of examining a relationship between the B content and weldingcrack, there occurred welding crack for the alloy containing B in anamount more than 0.0035 wt %. In this regard, Sample No. 1 has apossibility that there occurs slightly welding crack. As a result ofexamining an effect of the Mo content on the mechanical properties, thealloy containing Mo in an amount being as large as 1.18% exhibited ahigh creep rupture strength but an impact value lower than the requiredvalue. Meanwhile, the alloy containing Mo in an amount of 0.11 wt %exhibited a high toughness but a creep rupture strength lower than therequired value.

As a result of examining an effect of the W content on mechanicalproperties, the alloy containing W in an amount of 1.1 wt % exhibited avery high creep rupture strength, but the alloy containing W in anamount of 2 wt % or more exhibited a low impact absorption energy atroom temperature. In particularly, by adjusting a Ni/W ratio to be in arange of 0.25 to 0.75, there can be obtained a heat resisting cast steelcasing material satisfying characteristics required for high pressureand intermediate pressure inner casings, main steam stop valve casing,and steam governor valve casing of a high temperature/high pressureturbine used at a temperature of 621° C. or more and at a pressure of250 kgf/cm² or more, that is, exhibiting a 10⁵ h creep rupture strength(at 625° C.) of 9 kgf/mm² or more and an impact absorption energy (atroom temperature) of 1 kgf-m or more. In particular, by adjusting the Wcontent to be in a range of 1.2 to 2 wt % and the Ni/W ratio to be in arange of 0.25 to 0.75, there can be obtained a good heat resisting caststeel casing material exhibiting a 10⁵ h creep rupture strength (at 625°C.) of 10 kgf/mm² or more and an impact absorption energy (at roomtemperature) of 2 kgf-m or more.

                                      TABLE 14                                    __________________________________________________________________________                              625° C., 10.sup.5 h                                               Impact                                                                             creep                                                     Tensile   Reduction                                                                          absorption                                                                         rapture                                                   strength                                                                           Elongation                                                                         of area                                                                            energy                                                                             strength                                                                             Weld                                         Sample No.                                                                          (kgf/mm.sup.2)                                                                     (%)  (%)  (kgf-m)                                                                            Kgf/mm.sup.2)                                                                        cracking                                     __________________________________________________________________________    1     72.8 19.7 64.8 2.1  9.7    Presence                                     2     71.6 19.9 65.8 2.1  8.5    Absence                                      3     72.5 20.2 64.8 2.4  10     Absence                                      __________________________________________________________________________

The W content in a range of 1.0 wt % or more is significantly effectiveto increase the strength of the alloy. In particular, the alloycontaining W in an amount of 1.5 wt % or more exhibits a strength of 8.0kgf/mm² or more. Sample No. 7 was proved to sufficiently satisfy therequired strength at a temperature of 640° C. or less.

The inner casing of the high pressure/intermediate pressure portiondescribed in Embodiment 3 was produced by melting 1 ton of an alloymaterial having a specific composition of the heat resisting steel ofthe present invention in an electric furnace, followed by ladlerefining, and casting it in a sand mold. The casing thus obtained wassubjected to annealing (1050° C.×8 h→furnace cooling), and thensubjected to normalizing (1050° C.×8 h→air blast cooling) and temper(twice, 730° C.×8 h→furnace cooling +730° C.×8 h→furnace cooling). Thetrial casing having a full temper martensite structure was cut andexamined in terms of mechanical properties. As a result, it wasconfirmed that the casing sufficiently satisfies characteristics (10⁵ hcreep rupture strength (at 625° C.)≧9 kgf/mm² ; impact absorption energy(at 20° C.)≧1 kgf-m) required for a high temperature/high pressureturbine casing used at 250 atm and 625° C. and it is also weldable.

[Embodiment 6]

In this embodiment, the steam temperature in a high pressure steamturbine and an intermediate pressure steam turbine or a highpressure/intermediate pressure steam turbine is changed from 625° C. to649° C., and the structure and size of each steam turbine are designedto be substantially the same as those in Embodiment 2 or 3. Thisembodiment is different from Embodiment 2 in terms of the rotor shaft,first stage rotating blade, first stage stationary blade and innercasing, directly exposed to the above temperature atmosphere, of each ofthe high pressure steam turbine and the intermediate pressure steamturbine or the high pressure/intermediate steam turbine. As the materialfor the rotor shaft, first stage rotating blade and stationary blade,there is used such a material that the contents of B and Co in eachmaterial shown in Table 7 are increased to a value of 0.01 to 0.03 wt %and a value of 5 to 7 wt %, respectively. As the material for the innercasing, there is used such a material in which the content of W in eachmaterial in Embodiment 2 is increased to a value of 2 to 3 wt % andfurther Co is added to the material in an amount of 3 wt %. Each of therotor shaft, first stage rotating blade, stationary blade and innercasing made from the above materials satisfy the required strengths.This exhibits a large merit that the conventional design can be used asit is. That is to say, in this embodiment, by making all structuralmembers exposed to high temperatures from ferrite based steels, theconventional design thought can be adopted as it is. In addition, sincethe steam inlet temperatures of the second stage rotating blade andstationary blade are about 610° C., they are preferably made from thematerials used for the first stage rotating blade and stationary bladein Embodiment 1, respectively.

The steam temperature of the low pressure steam turbine is about 405°C., which is slightly higher than the steam temperature (about 380° C.)of the low pressure steam turbine in Embodiment 2 or 3, but the materialused for the rotor shaft in Embodiment 2 has the sufficiently highstrength, and accordingly, the same super clean material is used in thisembodiment.

The configuration of the cross compound type in this embodiment can beapplied to a tandem type having the number of revolution of 3600 rpm inwhich all of the steam turbines are directly connected to each other.

Industrial Applicability

According to the present invention, since a martensite based heatresisting cast steel having a high creep rupture strength at atemperature of 600 to 660° C. and a high toughness at room temperaturecan be obtained, main members for an ultrasuper critical pressureturbine at each temperature can be all made from ferrite based heatresisting steels, and consequently, there can be obtained a thermalpower-generation plant with a high reliability using the conventionalbasic design for the steam turbine as it is.

Conventionally, the member used at such a temperature has been requiredto be made from an austenite based alloy, and thereby a large-sizedrotor having a high quality has failed to be produced in terms ofproduction ability; however, a large-sized rotor having a high qualitycan be produced using a ferrite based heat resisting forged steel of thepresent invention.

The high temperature steam turbine made from full ferrite based steelsaccording to the present invention is advantageous in that the turbineis easy to rapidly start and is less susceptible to damages due tothermal fatigue because it does not use an austenite based alloy havinga large thermal expansion coefficient.

What is claimed is:
 1. A low pressure steam turbine including a rotor shaft, rotating blades planted in said rotor shaft, stationary blades for guiding flow of steam to said rotating blades, and an inner casing for holding said stationary blades, characterized in thatsaid rotating blades have a double-flow structure in which two sets, each being composed of five stages or more of said rotating blades, are symmetrically disposed right and left, and a first stage one of said rotating blades is planted at a central portion of said rotor shaft; said rotor shaft is made from a Ni--Cr--Mo--V based low alloy steel containing Cr in an amount of 1 to 2.5 wt % and Ni in an amount of 3.0 to 4.5 wt %, said rotor shaft being specified such that a distance (L) between centers of bearings provided for said rotor shaft is 6500 mm or more, the minimum diameter (D) of portions, of said rotor shaft, corresponding to said stationary blades is 750 mm or more, and the ratio (L/D) is in a range of 7.2 to 10.0; and a final stage one of said rotating blades is made from a high strength martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N, said final stage rotating blade being specified such that a value of [the length of a blade (inch)×the number of revolution (rpm)] is 125,000 or more.
 2. A low pressure steam turbine including a rotor shaft, rotating blades planted in said rotor shaft, stationary blades for guiding flow of steam to said rotating blades, and an inner casing for holding said stationary blades, characterized in thatthe temperature of a steam inlet to a first stage one of said rotating blades is in a range of 350 to 450° C.; and said rotor shaft is specified such that the diameter (D) of a portion, of said rotor shaft, corresponding to said stationary blade is in a range of 750 to 1000 mm and a distance (L) between centers of bearings provided for said rotor shaft is 7.2-10.0 times the diameter (D), said rotor shaft being made from a low alloy steel containing 0.2 to 0.3 wt % of C, 0.1 wt % or less of Si, 0.2 wt % or less of Mn, 3.2 to 4.0 wt % of Ni, 1.25 to 2.25 wt % of Cr, 0.1 to 0.6 wt % of Mo, and 0.05 to 0.25 wt % of V, the balance being 92.5 wt % or more of Fe.
 3. A low pressure steam turbine including a rotor shaft, rotating blades planted in said rotor shaft, stationary blades for guiding flow of steam to said rotating blades, and an inner casing for holding said stationary blades, characterized in that:said rotating blades having a double-flow structure in which two sets, each being composed of five stages or more of the rotating blades, are symmetrically provided right and left; the length of a blade portion of each of said rotating blades arranged from the upstream side to the downstream of the steam flow is in a range of 80 to 1300 mm; the diameter of said rotating blade planted portion of said rotor shaft is larger than the diameter of a portion, of said rotor shaft, corresponding to said stationary blade; the axial root width of said rotating blade portion is extended downward and is larger than the width of said rotating blade planted portion, and becomes stepwise larger from the upstream side to the downstream side; and the length of said axial root width of said rotating blade planted portion to the length of said blade portion is in a range of 0.20 to 1.60 and becomes gradually larger from the first stage and the preceding one of the final stage; and a final stage one of said rotating blades is made from a high strength martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N.
 4. A low pressure steam turbine including a rotor shaft, rotating blades planted in said rotor shaft, stationary blades for guiding flow of steam to said rotating blades, and an inner casing for holding said stationary blades, characterized in thatsaid rotating blades having a double-flow structure in which two sets, each being composed of five stages or more of the rotating blades, are symmetrically provided right and left; the length of a blade portion of each of said rotating blades arranged from the upstream side to the downstream of the steam flow is in a range of 80 to 1300 mm; and the ratio between the lengths of said blade portions of the adjacent ones of said rotating blades is in a range of 1.2 to 1.7 and the length of said blade portion of said rotating blade becomes larger from the upstream side to the downstream side; and a final stare one of said rotating blades is made from a high strength martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N.
 5. A low pressure steam turbine including a rotor shaft, rotating blades planted in said rotor shaft, stationary blades for guiding flow of steam to said rotating blades, and an inner casing for holding said stationary blades, characterized in thatsaid rotating blades having a double-flow structure in which two sets, each being composed of five stages or more of the rotating blades, are symmetrically provided right and left; the length of a blade portion of each of said rotating blades arranged from the upstream side to the downstream of the steam flow is in a range of 80 to 1300 mm; and the axial root width of said rotating blade planted portion of said rotor shaft becomes larger from the upstream side to the downstream side at least in three steps, and is extended downward and is larger the width of said rotating blade planted portion; and a final stage one of said rotating blades is made from a high strength martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N.
 6. A steam turbine rotating blade characterized in that said steam turbine blade is made from a martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N.
 7. A steam turbine rotating blade characterized in that said steam turbine blade is made from a martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of at least one of Nb and Ta, and 0.02 to 0.10 wt % of N; andthe tensile strength (at room temperature) of said martensite steel is 120 kgf/mm² or more; the length of a blade portion is 36 inches or more; and a value of ((the length of a blade (inch)×the number of revolution (rpm)) is 125,000 or more. 